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/plugins/cpptools/cpptools.qbs

@@ -14,6 +14,11 @@ QtcPlugin {
     Depends { name: "ProjectExplorer" }
     Depends { name: "app_version_header" }
 
+    pluginTestDepends: [
+        "CppEditor",
+        "QmakeProjectManager",
+    ]
+
     cpp.defines: base
     Properties {
         condition: qbs.toolchain.contains("msvc")