Add a new timeout option to set the HTTP Timeout

Adds a new --timeout option and check to the env
var OS_NETWORK_TIMEOUT to set the HTTP timeout used
for the request to the Neutron backend.

DocImpact

Closes-Bug: #1338932
Change-Id: I0d9687e671f68c4845af2439abfe581c6dcf020c
Merge "Add a new timeout option to set the HTTP Timeout"