Handle failures on update_dhcp_port

Ensure exceptions due to conflicting
state of network or subnet resources
are dealt with by the dhcp agent.

Closes-bug:  #1253344
Related-bug: #1243726

Change-Id: I4fd51442c034fabc91d5a3f065f4df98f5fad35b
Sync dhcp_agent.ini with the codes

Add an option item into dhcp_agent.ini to sync with the codes.
* Add ovs_integration_bridge in /etc/dhcp_agent.ini
* Add corresponding unit test

Change-Id: Ia78e7ca6c1fcbeca3e962f870a393e44183d719c
closes-Bug: #1256197
Fix downgrade in migration

In method downgrade_cisco in migration folsom_initial instead of
local method drop_tables op.drop_tables is used

Closes-Bug: #1243148

Change-Id: Ida6c52653c065e49c85141a7d1e61d394c1d709e
Change to improve dhcp-agent sync_state

Added a pool.waitall to dhcp-agent sync_state
to ensure that the last pool of threads are complete
before another sync_state begins.  Added another
log message to aid in debugging. Also added the
test_sync_state_waitall unit test.

Change-Id: I13d79a212672c4086e3082783743cb1ef2b48cfb
Closes-Bug: #1257514
Merge "Fix downgrade in migration"
Merge "Change to improve dhcp-agent sync_state"
Imported Translations from Transifex

Change-Id: I10900cbcfdd3e1568d48dc2e17ccb1a426cd27cb
Merge "Sync dhcp_agent.ini with the codes"
Merge "Handle failures on update_dhcp_port"