Comment 7 for bug 1556090

Reviewed: https://review.openstack.org/292016
Committed: https://git.openstack.org/cgit/openstack/networking-midonet/commit/?id=67e19d9ccc3fbc48d44065754dc0e0825f7e307f
Submitter: Jenkins
Branch: stable/liberty

commit 67e19d9ccc3fbc48d44065754dc0e0825f7e307f
Author: YAMAMOTO Takashi <email address hidden>
Date: Thu Dec 10 12:56:59 2015 +0900

    Clarify our use of Text(length) and explicitly restrict it to mysql

    Specify Text length only for mysql. Add a comment to explain
    why we specify this long length.

    SQLAlchemy mysql dialect uses the length argument of Text() to
    choose a backing type. (TEXT, LONGTEXT, ...)
    However Text() usually doesn't need the length argument and
    some dialects (eg. postgresql) bail out with errors when it's given.

    Also, remove the length argument from the model because it doesn't
    serve any purposes.

    Reference: http://docs.sqlalchemy.org/en/rel_1_0/core/type_basics.html#sqlalchemy.types.Text

    Backport note: This commit was edited to exclude test_migrations part.

    Closes-Bug: #1556090
    Change-Id: I78ae899df080a7aa1bb78ed75d8e43a9bf75103e
    (cherry picked from commit 11e7099788233d7281cb4ec67ea4ea9b0dbc1de9)
    Conflicts:
     midonet/neutron/tests/unit/db/test_migrations.py