Tighten flake8 checks in Gating

There are a few checks that already pass:
 - F401 - unused imports of modules
 - F403 - ‘from module import *’ used; unable to detect undefined names

And there are two (H401 and H403) that can be made
passing easily. Enable gating on all of them.

Change-Id: I9d3c49ecea1b2171d194ab6cc751316c252081e8
Datastore on Show Instance Should Not Be a Dict

From:

+-----------+-----------------------------------------------+
|  Property |                     Value                     |
+-----------+-----------------------------------------------+
|  created  |              2014-01-12T22:17:16              |
| datastore | {u'version': u'mysql-5.5', u'type': u'mysql'} |

To:

$ trove show 160e571f-afae-4ac8-aec0-7b2e55846e07
+-------------------+--------------------------------------+
|      Property     |                Value                 |
+-------------------+--------------------------------------+
|      created      |         2014-01-12T22:17:16          |
|     datastore     |                mysql                 |
| datastore_version |              mysql-5.5               |

Change-Id: I1542869760ab0010a2ada4ed16a0b526dc233220
Closes-Bug: #1254141
Merge "Tighten flake8 checks in Gating"
Merge "Datastore on Show Instance Should Not Be a Dict"