OFConnectionManager: OF 1.3 role request implementation

Largely the same as the nicira_role code, but just different enough that the
only common pieces are `ind_cxn_change_master` and `role_to_string`.

The full generation ID semantics are supported. The initial generation ID is
randomized to force controllers to request it.
Merge into master from pull request #62:
OFConnectionManager: OF 1.3 role request implementation (https://github.com/floodlight/indigo/pull/62)