Load only tested plugins when invoked with -test

By default, a clean settings path is used for test environment.

All the default plugins are loaded, although they're not needed.

This change significantly improves loading time for tests.

Change-Id: I24254f3e538e3f0e6d233d0989738dc1ce238209
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/libs/extensionsystem/optionsparser.cpp

@@ -91,6 +91,7 @@ bool OptionsParser::parse()
     }
     if (m_isDependencyRefreshNeeded)
         m_pmPrivate->resolveDependencies();
+    m_pmPrivate->enableOnlyTestedSpecs();
     return !m_hasError;
 }