Vcs: Move static functions out of VcsPlugin "namespace"

Plan is to split VcsPlugin in the pure IPlugin and a new class
the remaining non-IPlugin bits of VcsPlugin, call it VcsPluginPrivate
and use that d-ptr for VcsPlugin. VcsPlugin-derived classes can
then use VcsPluginPrivate derived private, later pointer members
of the *Privates can be made proper members, moving towards the
otherwise predominant plugin setup pattern.

Change-Id: I62db9269e8ca50633c24b6d1d735d59c8fa8e5a5
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/clearcase/clearcaseplugin.cpp

@@ -1453,7 +1453,7 @@ ClearCasePlugin::runCleartool(const QString &workingDir,
     }
 
     const SynchronousProcessResponse sp_resp =
-            VcsBasePlugin::runVcs(workingDir,
+                  VcsBase::runVcs(workingDir,
                                   {executable, arguments},
                                   timeOutS,
                                   flags, outputCodec);