clippy: do not fail the scan if clippy fails to install

If the `clippy` package is not available in the build repos, a warning
is emitted and `clippy` is not recorded as an enabled tool in the scan
properties.  But the scan continues without `clippy` in this case.

The approach is similar to what `--gcc-analyze` does.  This is needed
because `clippy` is not available for each mock config and we do not
want to configure the set of enabled tools separately for each mock
config.

py/plugins/clippy.py

@@ -1,6 +1,6 @@
 import os
 
-import csmock.common.util
+from csmock.common.util import write_toolver_from_rpmlist
 
 RUN_CLIPPY_CONVERT = "/usr/share/csmock/scripts/convert-clippy.py"
 CLIPPY_OUTPUT = "/builddir/clippy-output.txt"
@@ -28,14 +28,20 @@ def handle_args(self, parser, args, props):
         if not self.enabled:
             return
 
+        # install `clippy` only if the package is available in the build repos
+        props.install_opt_pkgs += ["clippy"]
+
         def inject_clippy_hook(results, mock):
-            return mock.exec_chroot_cmd(CLIPPY_INJECT_SCRIPT)
-        props.post_depinst_hooks += [inject_clippy_hook]
+            ec = write_toolver_from_rpmlist(results, mock, "clippy", "clippy")
+            if 0 != ec:
+                # a warning has already been emitted
+                return 0
 
-        props.install_pkgs += ["clippy"]
-        props.copy_out_files += [CLIPPY_OUTPUT]
+            # clippy was found in the buildroot -> instrument the build
+            props.copy_out_files += [CLIPPY_OUTPUT]
+            return mock.exec_chroot_cmd(CLIPPY_INJECT_SCRIPT)
 
-        csmock.common.util.install_default_toolver_hook(props, "clippy")
+        props.post_depinst_hooks += [inject_clippy_hook]
 
         def convert_hook(results):
             src = f"{results.dbgdir_raw}{CLIPPY_OUTPUT}"