Add configurable http_timeout parameter for Cisco N1K

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

Closes-Bug: #1332290
Change-Id: I429dd9efa43f6a596933359f4627a7761411e621
Merge "Add configurable http_timeout parameter for Cisco N1K"