rdbms: make getMasterPos() ignore GTIDs outside of gtid_domain_id

rdbms: make getMasterPos() ignore GTIDs outside of gtid_domain_id

* Filter out GTIDs with a domain that is not the one binlog
  events would be written to if the Database handle was given
  write queries. Likewise for the MariaDB server_id component.
* Also improve MySQL GTID support to better match that of MariaDB.
  This covers position retrieval, replication waiting, and ranges
  in GTIDs (which are almost always present).
* Make some MySQLMasterPos variables private by making use of
  accesors instead.
* Store the gtids array keyed by domain ID for convenience.
* Clean up dynamic call to static method.

Change-Id: Ic6ab517bc8f200c968ff892ade69ad1b9394ab21