Properly process plugin attributes in default handler

Patch fixes default workflow from CLI, which is:
fuel attributes --env 1 --default
Gets you default attributes for your env, then you are able
to enable/disable plugin and
fuel attributes --env 1 --upload
Upload them back

related to blueprint cinder-neutron-plugins-in-fuel

Change-Id: I805d53f5adfefca4c72662c143d9a5474a98e862
Merge "Properly process plugin attributes in default handler"