Do not drop appengine api when converting old-style library container

[chanseokoh]

Fixes #3202.

[codecov]

Codecov Report

Merging #3214 into master will increase coverage by 0.2%.
The diff coverage is 28.57%.

@@             Coverage Diff             @@
##             master    #3214     +/-   ##
===========================================
+ Coverage     70.05%   70.25%   +0.2%     
- Complexity     2971     2989     +18     
===========================================
  Files           374      374             
  Lines         13533    13583     +50     
  Branches       1624     1638     +14     
===========================================
+ Hits           9480     9543     +63     
+ Misses         3376     3365     -11     
+ Partials        677      675      -2

Impacted Files	Coverage Δ	Complexity Δ
.../compat/cte13/CloudToolsEclipseProjectUpdater.java	79.24% <ø> (-0.39%)	11 <0> (ø)
...t/cte13/UpdateCloudToolsEclipseProjectHandler.java	9.09% <0%> (-0.91%)	1 <0> (ø)
.../appengine/localserver/launching/LaunchHelper.java	48.19% <50%> (+0.63%)	15 <0> (-1)	⬇️
...calAppEngineServerLaunchConfigurationDelegate.java	61.42% <0%> (-0.3%)	39% <0%> (ø)
...ow/ui/preferences/RunOptionsDefaultsComponent.java	78.57% <0%> (+0.62%)	60% <0%> (+2%)	⬆️
...ls/eclipse/appengine/newproject/CodeTemplates.java	95.7% <0%> (+1.49%)	45% <0%> (+13%)	⬆️
...com/google/cloud/tools/eclipse/util/Templates.java	87.5% <0%> (+5.68%)	4% <0%> (ø)	⬇️
...ipse/dataflow/core/project/DataflowMavenModel.java	63.88% <0%> (+9.72%)	9% <0%> (ø)	⬇️
...aflow/ui/handler/ModifyDataflowVersionHandler.java	20.83% <0%> (+20.83%)	2% <0%> (+2%)	⬆️

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[elharo]

Should we cut with this included?