CI integration tests don't fail on non-fatal mixin errors

[zml2008]

It seems some Mixin errors are considered 'non-fatal' and won't actually kill the process. Will need to hook into Mixin error handling to properly fail the build for these.

Example (from #3332):

[21:43:23] [main/INFO] [c.mod.mod.LaunchServiceHandler/MODLAUNCHER]: Launching target 'sponge_server_it' with arguments [--nogui]
[21:43:25] [main/ERROR] [mixin]: mixins.sponge.api.json:mcp.server.ServerScoreboardMixin_API: getObjective does not exist in target interface org.spongepowered.api.scoreboard.Scoreboard
org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: getObjective does not exist in target interface org.spongepowered.api.scoreboard.Scoreboard
	at org.spongepowered.asm.mixin.transformer.InterfaceInfo.renameMethod(InterfaceInfo.java:188) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.prepareSoftImplements(MixinPreProcessorStandard.java:224) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.prepareMethod(MixinPreProcessorStandard.java:205) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.prepare(MixinPreProcessorStandard.java:184) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinInfo$State.validateChanges(MixinInfo.java:438) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinInfo$State.validate(MixinInfo.java:340) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinInfo.validate(MixinInfo.java:903) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinConfig.postInitialise(MixinConfig.java:672) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinProcessor.prepareConfigs(MixinProcessor.java:542) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinProcessor.select(MixinProcessor.java:439) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinProcessor.checkSelect(MixinProcessor.java:415) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:285) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:223) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.mixin.transformer.MixinTransformationHandler.processClass(MixinTransformationHandler.java:121) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at org.spongepowered.asm.launch.MixinLaunchPlugin.processClass(MixinLaunchPlugin.java:131) ~[mixin-0.8.2.jar:0.8.2+unknown-b0.git-unknown]
	at cpw.mods.modlauncher.serviceapi.ILaunchPluginService.processClassWithFlags(ILaunchPluginService.java:154) ~[modlauncher-8.0.9.jar:8.0.9+86+master.3cf110c]
	at cpw.mods.modlauncher.LaunchPluginHandler.offerClassNodeToPlugins(LaunchPluginHandler.java:85) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.ClassTransformer.transform(ClassTransformer.java:120) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.TransformingClassLoader$DelegatedClassLoader.findClass(TransformingClassLoader.java:265) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.TransformingClassLoader.loadClass(TransformingClassLoader.java:136) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.TransformingClassLoader.loadClass(TransformingClassLoader.java:98) ~[modlauncher-8.0.9.jar:?]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:522) ~[?:?]
	at java.lang.Class.forName0(Native Method) ~[?:?]
	at java.lang.Class.forName(Class.java:468) ~[?:?]
	at org.spongepowered.vanilla.applaunch.handler.test.ServerTestLaunchHandler.launchService0(ServerTestLaunchHandler.java:42) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	at org.spongepowered.vanilla.applaunch.handler.AbstractVanillaLaunchHandler.lambda$launchService$1(AbstractVanillaLaunchHandler.java:162) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:82) ~[modlauncher-8.0.9.jar:?]
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) ~[modlauncher-8.0.9.jar:?]
	at org.spongepowered.vanilla.applaunch.Main.run(Main.java:91) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	at org.spongepowered.vanilla.applaunch.Main.main(Main.java:62) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	... suppressed 3 lines
	at java.lang.reflect.Method.invoke(Method.java:564) ~[?:?]
	at org.spongepowered.vanilla.installer.InstallerMain.invokeMain(InstallerMain.java:107) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	at org.spongepowered.vanilla.installer.InstallerMain.run(InstallerMain.java:100) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]
	at org.spongepowered.vanilla.installer.InstallerMain.main(InstallerMain.java:64) ~[spongevanilla-1.16.5-8.0.0-RC0-universal.jar:1.16.5-8.0.0-RC0]