Add support for Bugzilla Tokens

- if login provides a token, reuse it for all subsequent requests sent
  to that domain
- changes are transparent to user
- persist tokens in ~/.bugzillatoken
- ensure test cases are aware of tokens

(crobinso: The RPC key name we need to set is actually Bugzilla_token)
Minor cleanups to previous patch to apease pylint
Bugzilla: Add tokenfile= init parameter

Allows users to control where the tokenfile is, and whether to save tokens
at all. Similar to the cookiefile parameter.
bugzilla: Add --tokenfile option

Similar to --cookiefile
rw_functional: Use bugzilla.redhat.com for cookietest
Ensure Bugzilla_token is set when no args present

Thanks to Simon Baird for pointing out the issue.