Bug #1250738: Galera tests are skipped on some Jenkins slaves with
              galera55 configuration

The problem was that Galera tests checked for Galera support by starting
temporary mysqld instances without specifying a configuration file. On
some Jenkins slaves (e.g. Ubuntu ones in our cluster) there was a
default configuration file at /etc/mysql/my.cnf which had query_cache
enabled. Since query_cache is not supported by Galera, the server
refused to start, so Galera support checks in tests assumed it there is
no support and skipped the tests.

Fixed by changing the way Galera support is being detected by the test
suite. Instead of each tests having to roll its own check with a
temporary mysqld instance, run.sh performs this check on startup by
checking the wsrep_ready status variable (along with other
version-specific variables). The value of that variable is then
exported to subshells, so it is available to tests. As an extra safety,
run.sh will also abort with an error, if Galera testing was explicitly
requested via -c galera55.
Bug #1049291: innobackupex --copy-back fails with an empty
              innodb-data-home-dir

The problem was that innobackupex unconditionally required
innodb-data-home-dir to exist and be empty. There are, however, cases
when the value of that variable does not represent a valid path (it may
be empty), or point to root directory ("/") which naturally cannot be
empty.

Solutions:

- do not perform any checks for an empty innodb-data-home-dir

- assume an empty innodb-data-home-dir to be identical to MySQL’s
datadir to replicate InnoDB behavior

- do not require innodb-data-home-dir to be empty, but instead refuse to
existing files in that directory. The non-empty requirement for the
data directory makes sense, it was implemented to fix bug
#737569. Requiring other directories to be empty is redundant, it is
sufficient to just refuse to overwrite any files.

The above changes, together with some previous bugfixes, automatically
fix bug #382742. So this patch adds a test case for that bug.
Addendum to
https://blueprints.launchpad.net/percona-xtrabackup/+spec/links-to-percona-site

Added blank lines to make distribution message more distinct.
Merged lp:~akopytov/percona-xtrabackup/bug1049291-2.1.
Bug #1164945: move-back/copy-back should allow non-empty directories in
              some cases

The patches introduces a new innobackupex option,
--force-non-empty-directories. When specified, it makes --copy-back or
--move-back transfer files to non-empty directories. Note that no
existing files will be overwritten. If --copy-back or --nove-back has to
copy a file from the backup directory which already exists in the
destination directory, it will still fail with an error.
Merged lp:~akopytov/percona-xtrabackup/bug1250738-2.1.
Merged lp:~akopytov/percona-xtrabackup/bug1049291-2.1.
Merged lp:~akopytov/percona-xtrabackup/bug1164945-2.1.
- release notes for 2.1.6