http_timeout is a constant defined in the code. This change makes it
configurable by providing it as an option in the config file.
DocImpact
Conflicts:
etc/neutron/plugins/cisco/cisco_plugins.ini
neutron/plugins/cisco/common/config.py
Closes-Bug: #1332290
Change-Id: I429dd9efa43f6a596933359f4627a7761411e621
(cherry picked from commit a8d67485ab)