Drop RpcProxy usage from bigswitch plugin

This patch drops the usage of the RpcProxy compatibility class from
the bigswitch plugin.  The equivalent usage of oslo.messaging APIs is
now used instead.

Note that there is one very minor functional change included.  The
previous code set the base version to '1.1'.  It should be '1.0'.  The
proper pattern to use is to set the base version on the client side to
be the initial version of the API (X.0).  Then, any methods that
require a newer version need to specify it.  In this case, verison
'1.1' was the security group methods, and those specify '1.1' as you
would expect.

Part of blueprint drop-rpc-compat.

Change-Id: I695d2a26db9c01b0be65b11cd4e4063567b5f20d
Merge "Drop RpcProxy usage from bigswitch plugin"