Implement greeting_encode()/greeting_decode() functions

 * Update iproto.cc to use greeting_encode()
 * Update replica.cc and net.box to use greeting_decode()
 * Add a parsed remote version to net.box and struct replica
 * Remove duplicate code

Protocol change:

 * During binary protocol handshake sent
    "Tarantool 1.6.7-83-gc6b2129 (Binary)" instead of
    "Tarantool 1.6.7-83-gc6b2129              @custom_proc_title"
   This change is backward-compatible up to 1.6.1.