new poisoned plugin cache and various fixes

- generate .poisonededmplugincache for following. Plugin manager reads this information and make sure that it always load a plugin from local area if it was suppose to be build locally. 
  * locally build packages
  * locally deleted packages
- Remove unused SHARED_LIB_LOAD_CHECK 
- SCRAM now prefix all unittests with $(SCRAM_TEST_RUNNER_PREFIX)