Big Switch: Only update hash header on success

This patch moves the hash update call into the success block
of the server manager so the database isn't updated with
a hash header from an error response. Additionally, it prevents
the hash from being updated to an empty value if the hash header
is not present in the response.

Conflicts:

	neutron/tests/unit/bigswitch/test_servermanager.py

Closes-Bug: #1348766
Change-Id: I512d01f9bb91b208dd58883d2464951ecc6748e1
(cherry picked from commit b8cf45218714937681d7df2e5b9d7d440cb2edd9)
Remove explicit dependency on amqplib

kombu already depends on amqp or amqplib depending on its
version, and no explicit access to amqplib exists in neutron code.

Conflicts:
	requirements.txt

Closes-Bug: #1317094
Change-Id: I5cf189d7173b732cba6df3f9b6aff1d2bb85cdfe
(cherry picked from commit 39ffcb0dd75d9dc5d8a249f2974a67f0def5204b)
Merge "Big Switch: Only update hash header on success" into stable/icehouse
Merge "Remove explicit dependency on amqplib" into stable/icehouse
Merge branch 'stable/icehouse' of https://github.com/openstack/quantum into stable/icehouse

Conflicts:
	neutron/plugins/bigswitch/servermanager.py
	neutron/tests/unit/bigswitch/test_servermanager.py