We also hit it this morning with icehouse and trusty:

2015-09-17 12:57:30 INFO install Setting up galera-3 (25.3.12-1trusty) ...
2015-09-17 12:57:30 INFO install Setting up libhtml-template-perl (2.95-1) ...
2015-09-17 12:57:30 INFO install Processing triggers for libc-bin (2.19-0ubuntu6.6) ...
2015-09-17 12:57:30 INFO install Processing triggers for ureadahead (0.100.0-16) ...
2015-09-17 12:57:32 INFO install  * MySQL server PID file could not be found!
2015-09-17 12:57:32 INFO install Starting MySQL
2015-09-17 12:57:39 DEBUG juju.worker.leadership tracker.go:138 galera-cluster/0 renewing lease for galera-cluster leadership
2015-09-17 12:57:39 DEBUG juju.worker.leadership tracker.go:165 checking galera-cluster/0 for galera-cluster leadership
2015-09-17 12:57:39 DEBUG juju.worker.leadership tracker.go:180 galera-cluster/0 confirmed for galera-cluster leadership until 2015-09-17 12:58:39.535692631 +0000 UTC
2015-09-17 12:57:39 INFO juju.worker.leadership tracker.go:182 galera-cluster/0 will renew galera-cluster leadership at 2015-09-17 12:58:09.535692631 +0000 UTC
2015-09-17 12:57:42 INFO install .......... * 
2015-09-17 12:57:42 INFO worker.uniter.jujuc server.go:158 running hook tool "juju-log" ["-l" "DEBUG" "Using existing password file '/var/lib/charm/galera-cluster/mysql.passwd'"]
2015-09-17 12:57:43 DEBUG worker.uniter.jujuc server.go:159 hook context id "galera-cluster/0-install-7730906871290845817"; dir "/var/lib/juju/agents/unit-galera-cluster-0/charm"
2015-09-17 12:57:43 DEBUG juju-log Using existing password file '/var/lib/charm/galera-cluster/mysql.passwd'
2015-09-17 12:57:44 INFO worker.uniter.jujuc server.go:158 running hook tool "juju-log" ["-l" "DEBUG" "Opening db connection for root@localhost"]
2015-09-17 12:57:44 DEBUG worker.uniter.jujuc server.go:159 hook context id "galera-cluster/0-install-7730906871290845817"; dir "/var/lib/juju/agents/unit-galera-cluster-0/charm"
2015-09-17 12:57:44 DEBUG juju-log Opening db connection for root@localhost
2015-09-17 12:57:44 INFO install Traceback (most recent call last):
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/install", line 444, in <module>
2015-09-17 12:57:44 INFO install     main()
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/install", line 438, in main
2015-09-17 12:57:44 INFO install     hooks.execute(sys.argv)
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/charmhelpers/core/hookenv.py", line 544, in execute
2015-09-17 12:57:44 INFO install     self._hooks[hook_name]()
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/install", line 99, in install
2015-09-17 12:57:44 INFO install     configure_sstuser(mysql_password)
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/galera_utils.py", line 158, in configure_sstuser
2015-09-17 12:57:44 INFO install     m_helper.execute(SQL_SST_USER_SETUP.format(sst_password))
2015-09-17 12:57:44 INFO install   File "/var/lib/juju/agents/unit-galera-cluster-0/charm/hooks/charmhelpers/contrib/database/mysql.py", line 134, in execute
2015-09-17 12:57:44 INFO install     cursor.execute(sql)
2015-09-17 12:57:44 INFO install   File "/usr/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 174, in execute
2015-09-17 12:57:44 INFO install     self.errorhandler(self, exc, value)
2015-09-17 12:57:44 INFO install   File "/usr/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
2015-09-17 12:57:44 INFO install     raise errorclass, errorvalue
2015-09-17 12:57:44 INFO install _mysql_exceptions.OperationalError: (1047, 'Unknown command')
2015-09-17 12:57:44 INFO juju.worker.uniter.context context.go:543 handling reboot
2015-09-17 12:57:44 ERROR juju.worker.uniter.operation runhook.go:103 hook "install" failed: exit status 1
2015-09-17 12:57:44 DEBUG juju.worker.uniter modes.go:31 [AGENT-STATUS] failed: run install hook
2015-09-17 12:57:44 INFO juju.worker.uniter modes.go:543 ModeContinue exiting
2015-09-17 12:57:44 INFO juju.worker.uniter modes.go:541 ModeHookError starting
2015-09-17 12:57:44 DEBUG juju.worker.uniter.filter filter.go:597 want resolved event
2015-09-17 12:57:44 DEBUG juju.worker.uniter.filter filter.go:591 want forced upgrade true
2015-09-17 12:57:44 DEBUG juju.worker.uniter.filter filter.go:727 no new charm event
2015-09-17 12:57:44 DEBUG juju.worker.uniter modes.go:31 [AGENT-STATUS] error: hook failed: "install"