Fix segment allocation tables in Cisco N1kv plugin

The segment allocation table is emptied on deleting any network profile.
This change allows the use of segment range from the network profile table.
By using the network profile UUID as a foreign key in the segment allocations table,
tables are cleaned up only for the segments associated with
the deleted network profile via CASCADE, leaving no inconsistencies.

Change-Id: I507041fac3768a7b688ddcf28c4d97c618bfe3f9
Closes-Bug: #1288407
Disable XML tests on Py26

Unit testing on Py26 takes too long to run.  The code paths are the
same, so we'll temporarily skip tests is the class contains XML
formating since duplicate full stack JSON tests are run.

Change-Id: Ie8eddfe0b6af39f32380ce532e0c26acc0a6596d
Related-Bug: 1295281
Fix namespace exist() method

Fix namespace exist() method for it shall not be called with a root.
Also, don't run it under the namespace so garbage_collect_namespace
method can run without rootwrap and not withi a ns.

As a result of fixing namespace listing the patch also fixes the
regression introduced (bug/1294603) to loadbalancer agent respawning
haproxy due to inability to list namespaces properly.

Change-Id: I0dc4d01b0c1c04887ec6ad5766ec7c6c96903faa
Closes-Bug: #1297594
Closes-Bug: #1294603
Merge "Fix segment allocation tables in Cisco N1kv plugin"
Merge "Fix namespace exist() method"
Merge "Disable XML tests on Py26"