Fixing API breakage
Cleanup of itests to not influence each other when setting server identity
and manipulating plugins.

Also fixed the PluginManagerBeanTest#isPluginReadyForPurge() by realizing
that other tests (that now correctly clean up after themselves) may have
already deleted the plugins that were marked to be deleted in the test
method the isPluginReadyForPurge depends on.
Removed unused method from local SLSB and some small docs updates.