Rename --timeout global option and make it work

The --timeout option doesn't work for standalone use-cases when
you specify no-client-auth, and it's also confusing since it's
easily misinterpreted as an option related to the heat timeouts
provided to stack-create and in future stack-update.

So take this opportunity to rename the option to --api-timeout,
which hopefully more accurately reflects it's purpose, and don't
pass a default (just let requests use the global default socket
timeout) as it seems relatively unlikely users will wait for 10
minutes before pressing Ctrl-C on interactive shell requests.

Change-Id: I52480f0d128735bf5f312fc88f4078f27717baf2
Partial-Bug: #1290456