Most of the mtr tests in the galera_3nodes suite fail
for a variety of reasons with a variety of errors.

This patch fixes several substantial flaws
in the galera_3nodes suite tests and in the mtr framework
service files, adapting the tests from galera_3nodes
for the current version of MariaDB.

This patch also synchronizes some galera_3nodes-related
files with the latest changes made for MDEV-17835 (v2 patch)
and for MDEV-18379 in other branches (10.2 and 10.3).

Closes #1161

When importing a tablespace, we must initialize dummy DEFAULT NULL
values for any instantly added columns in order to avoid a debug
assertion failure when PageConverter::update_records() invokes
rec_get_offsets(). Finally, when the operation completes, we must
evict and reload the table definition, so that the correct
default values for instantly added columns will be loaded.

ha_innobase::discard_or_import_tablespace(): On successful
IMPORT TABLESPACE, evict and reload the table definition,
so that btr_cur_instant_init() will load the correct metadata.

PageConverter::update_index_page(): Fill in dummy DEFAULT NULL values
for instantly added columns. These will be replaced upon the
completion of the operation by evicting and reloading the metadata.

row_discard_tablespace(): Invoke dict_table_t::remove_instant().
After DISCARD TABLESPACE, the table is no longer in "instant ALTER"
format, because there is no data file attached.

The code path where the table was not being rebuilt during ALTER TABLE
was not covered by the test. Add coverage, and remove the debug assertion
that could fail in this case.

Followup for db8f0dae

and in fef9013d

fixes memory leaks in restart_mysqld.inc tests

Followup for 8f5ea83f

MDEV-18426: Most of the mtr tests in the galera_3nodes suite fail

- Fixes building with galera and tokudb
- Added support for --without-wsrep BUILD script option

- Backport from 10.4

Most of the mtr tests in the galera_3nodes suite fail
for a variety of reasons with a variety of errors.
Some tests simply need to add the missing "connection"
lines to the result files, but many of them fail due
to substantial errors that require reworking test files.

This patch adds the missing "connection" lines to
the result files and fixes several substantial flaws
in the galera_3nodes suite tests and in the mtr framework
service files, adapting the tests from galera_3nodes
for the current version of MariaDB.

https://jira.mariadb.org/browse/MDEV-18426

According to close(2) "Retrying the close() after a failure return is
the wrong thing to do"

Corrects 5c81cb88 in MDEV-15635