MDEV-6196 MTR: Do not hardcode path for libgalera_smm.so

Introduced an environment variable WSREP_PROVIDER to point
to the galera library.

Updated the tests.

mysql-test/mysql-test-run.pl

@@ -2393,6 +2393,22 @@ sub environment_setup {
     $ENV{'NDB_EXAMPLES_OUTPUT'}=      $path_ndb_testrun_log;
   }
 
+  # ----------------------------------------------------
+  # Setup env for wsrep
+  # ----------------------------------------------------
+  if (defined $ENV{'WSREP_PROVIDER'} )
+  {
+    # Nothing needs to be done! WSREP_PROVIDER env is already set and will be
+    # used.
+  } else {
+    my $file_wsrep_provider=
+      mtr_file_exists("/usr/lib/galera/libgalera_smm.so",
+                      "/usr/lib64/galera/libgalera_smm.so");
+    $ENV{'WSREP_PROVIDER'}=  $file_wsrep_provider;
+  }
+  
+  mtr_verbose("WSREP_PROVIDER set to $ENV{'WSREP_PROVIDER'}");
+
   # ----------------------------------------------------
   # mysql clients
   # ----------------------------------------------------

mysql-test/suite/galera/galera_2nodes.cnf

@@ -3,12 +3,12 @@
 
 [mysqld.1]
 binlog-format=row
-wsrep_provider=/usr/lib/galera/libgalera_smm.so
+wsrep_provider=@ENV.WSREP_PROVIDER
 wsrep_cluster_address='gcomm://'
 
 [mysqld.2]
 binlog-format=row
-wsrep_provider=/usr/lib/galera/libgalera_smm.so
+wsrep_provider=@ENV.WSREP_PROVIDER
 wsrep_cluster_address='gcomm://127.0.0.1:4567'
 wsrep_provider_options='gmcast.listen_addr=tcp://127.0.0.1:4568'
 

mysql-test/suite/wsrep/t/binlog_format.opt

---binlog-format=row --innodb_autoinc_lock_mode=2 --innodb_locks_unsafe_for_binlog=1 --wsrep-provider=/usr/lib/galera/libgalera_smm.so  --wsrep-cluster-address=gcomm:// --wsrep-on=1 --log-bin
+--binlog-format=row --innodb_autoinc_lock_mode=2 --innodb_locks_unsafe_for_binlog=1 --wsrep-provider=$WSREP_PROVIDER --wsrep-cluster-address=gcomm:// --wsrep-on=1 --log-bin

mysql-test/suite/wsrep/t/pool_of_threads.opt

---binlog-format=row --innodb_autoinc_lock_mode=2 --innodb_locks_unsafe_for_binlog=1 --wsrep-provider=/usr/lib/galera/libgalera_smm.so --wsrep-cluster-address=gcomm:// --thread_handling=pool-of-threads
+--binlog-format=row --innodb_autoinc_lock_mode=2 --innodb_locks_unsafe_for_binlog=1 --wsrep-provider=$WSREP_PROVIDER --wsrep-cluster-address=gcomm:// --thread_handling=pool-of-threads