Reflect comments from any table accessible by the current user

Reflect comments from any table accessible by the current user

Fixed a reflection bug where table comments could only be retrieved for
tables actually owned by the user but not for tables visible to the user
but owned by someone else.  Pull request courtesy Dave Hirschfeld.

Fixes: #5146
Closes: #5147
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5147
Pull-request-sha: 0651e3bed05923765203b37986a2506dac3e634e

Change-Id: If970fda10d6adf04d926d38df1a567df1de9f7b9
(cherry picked from commit 0c294d356f7cbb22a8da3fc4552a9c4232c3f69a)