Change variable name of admin_state_down to admin_state

It is confusing that admin_state_down=False means admin-state is DOWN.
It is easy to understand if the variable name matches its value.

Also removes 'default=xxx' from options with store_true/false action
since store_true/false sets the default value implicitly.

Fixes bug 1161853

Change-Id: I3146dd8974990c94e5f9b3b5bf6a8b28a245d64e
Merge "Change variable name of admin_state_down to admin_state"