Perl Plugin: changed exec in provider 'false' case:

perl -M${module} -e 1 does not work here because of two Problems:

1. $include_dirs is ignored
2. Collectd.pm boundled with collectd uses constants, which are set by the special perl interpreter
   build into collectds perl plugin.
   Without these constants collectd perl modules will not work.

This commit fixes both issues.

manifests/plugin/perl/plugin.pp

@@ -68,7 +68,11 @@
     }
     false: {
       # this will fail if perl collectd plugin module is not installed
-      exec { "perl -M${module} -e 1": path => $::path }
+      $include_dirs_prefixed = prefix($include_dirs, '-I')
+      $include_dirs_prefixed_joined = join($include_dirs_prefixed,' ')
+      exec { "perl ${include_dirs_prefixed_joined} -e 'my\$m=shift;eval\"use \$m\";exit!exists\$INC{\$m=~s!::!/!gr.\".pm\"}' ${module}":
+        path => $::path
+      }
     }
     default: {
       fail("Unsupported provider: ${provider}. Use 'package', 'cpan',