This is redesign of plugins architecture in order to store
the plugin's attributes in a separate table, not in cluster
attributes, so it will be possible to remove connection between
plugin and cluster when a plugin gets deleted.
Added ability to work with different versions of a plugin.
User can choose the preferred version in UI.
The test "test_plugin_generator" was removed because no longer
relevant.
Closes-Bug: #1440046
Implements: blueprint store-plugins-attributes
Change-Id: I52115f130bf1c7c80c66e18d0bf9f7acb16dd56c