Move extension system auto tests.

src/libs/extensionsystem/test/extensionsystem_test.pri

-RELATIVEPATH = $$RELATIVEPATH/../../../..
-INCLUDEPATH *= $$PWD/../..
-macx {
-    LIBS += -L"$$OUT_PWD/$$RELATIVEPATH/bin/Qt Creator.app/Contents/PlugIns"
-}
-else {
-    LIBS += $$OUT_PWD/$$RELATIVEPATH/lib
-}
-
-# stolen from qtcreator.pri
-defineReplace(qtLibraryName) {
-   unset(LIBRARY_NAME)
-   LIBRARY_NAME = $$1
-   CONFIG(debug, debug|release) {
-      !debug_and_release|build_pass {
-          mac:RET = $$member(LIBRARY_NAME, 0)_debug
-              else:win32:RET = $$member(LIBRARY_NAME, 0)d
-      }
-   }
-   isEmpty(RET):RET = $$LIBRARY_NAME
-   return($$RET)
-}
-
-include(../extensionsystem.pri)
-
-QT *= xml
-