MDEV-6247: Merge 10.0-galera to 10.1.

Merged lp:maria/maria-10.0-galera up to revision 3867.
Review fixes.
Fix Windows compiler errors.
Fix merge error.
Fix merge errors.
Merge lp:maria/maria-10.0-galera revisions 3867..3869 and
3871..3879.
Add missing test files for new configuration variables.

Added a new functions to handler API to forcefully abort_transaction,
producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
were added for future possiblity to add more storage engines that
could use galera replication.
MDEV-6247: Merge 10.0-galera to 10.1.

Merged lp:maria/maria-10.0-galera up to revision 3879.

Added a new functions to handler API to forcefully abort_transaction,
producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
were added for future possiblity to add more storage engines that
could use galera replication.
Merge branch 'bb-10.1-galera' of github.com:MariaDB/server into bb-10.1-galera
MDEV-6247: Merge 10.0-galera to 10.1.

    Merged lp:maria/maria-10.0-galera up to revision 3880.

    Added a new functions to handler API to forcefully abort_transaction,
    producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
    were added for future possiblity to add more storage engines that
    could use galera replication.