Filter out extra-specs from type get for non-admin

Filter out extra-specs from type get for non-admin

Currently when a get_volume type call is made to the
db api, we don't check context and auto-fill the
extra-specs info for that type.

Extra specs are intended to be admin only info, but anybody
that calls the API directly to list or get volume-types is
also given this info which is not intended.

This patch just adds a context check to the db api's
private extra-specs builder method.  In the case of
non-admin, we just skip adding the extra-specs.

Change-Id: Ia46695a6c890c06d94e6903ed9c54794107fa132
Closes-Bug: #1351971
Closes-Bug: #1475285