Apply six for metaclass

__metaclass__ cannot be used in python3.
six be used in general for python 3 compatibility.

Change-Id: I1d21c82163a1c00bbf4fbf3c9dd513f1c0591b00
Closes-Bug: #1236648
Add cinder.db.migration.db_initial_version()

Updates Cinder to use a new function called db_initial_version()
instead of the INIT_VERSION constant. This allows us to
move the top level INIT_VERSION constant into the
sqlalchemy migration.py implementation where it belongs.

Change-Id: I10dacdebb50d3121e3bfd094e40138807233aa64
Add missing space to num_iser_scan_tries text

Should read "...rescan iSER target to" rather than
"targetto".

Change-Id: I785f67f3a029f06c0184762ddf795202ae198397
Merge "Add cinder.db.migration.db_initial_version()"
Merge "Apply six for metaclass"