IPROTO_VOTE command - follow-up fixes

This patch contains some follow-up fixes for fe8ae607
("Introduce IPROTO_VOTE command"):
 - Rename 'status' to 'ballot' everywhere in the comments.
 - Rename IPROTO_REQUEST_VOTE to IPROTO_VOTE_DEPRECATED and
   iproto_reply_request_vote to iproto_reply_vote_deprecated
   to emphasize the fact that this iproto command has been
   deprecated and IPROTO_VOTE should be used instead.
 - Only send an IPROTO_VOTE request to a master if it is
   running tarantool 1.10.1 or newer.