BUG#25147154 : MTR TRIES TO COPY CONTENTS FROM /TMP/DATA

Description :
=============
When a MTR test run is started, it initializes the server and creates
the datadir under '$MYSQL_TEST_DIR/var'('/tmp/var' or '/dev/shm/var'
if --mem option is used) location and then copies it to the datadir
location of server(s).

If $parallel == 1, datadir location of the server is
'$MYSQL_TEST_DIR/var/data'. If $parallel > 1, datadir location of any
server is '$MYSQL_TEST_DIR/var/<thread_num>/data'.

This is the reason MTR searches for the initialized datadir in 2
locations('$opt_vardir' and '$opt_vardir/..') from the current vardir
location..

But this can cause few problems. If a directory with the name 'data'
already exists under '$MYSQL_TEST_DIR' and if the MTR run is started
with parallel value 1, then

1. copytree($install_db, '$opt_vardir/..') command will fail if the
user doesn't have the access permission to '$MYSQL_TEST_DIR/data'
directory.
2. Unnecessary contents from '$MYSQL_TEST_DIR/data' directory will be
copied to server datadir location and this might affect the server
startup.

Fix :
=====
Depending on the $parallel value decide whether the path for the
initialize datadir is "$opt_vardir"(i.e $parallel = 1) or
"$opt_vardir/.."(i.e $parallel > 1).
Reviewed-by: Deepa Dixit <deepa.dixit@oracle.com>
Reviewed-by: Srikanth B R <srikanth.b.r@oracle.com>
RB: 14773

mysql-test/mysql-test-run.pl

@@ -5388,16 +5388,14 @@ sub start_servers($) {
     my $mysqld_basedir= $mysqld->value('basedir');
     if ( $basedir eq $mysqld_basedir )
     {
-      if (! $opt_start_dirty)	# If dirty, keep possibly grown system db
+      if (!$opt_start_dirty)	# If dirty, keep possibly grown system db
       {
-	# Copy datadir from installed system db
-	for my $path ( "$opt_vardir", "$opt_vardir/..") {
-	  my $install_db= "$path/install.db";
-	  copytree($install_db, $datadir)
-	    if -d $install_db;
-	}
-	mtr_error("Failed to copy system db to '$datadir'")
-	  unless -d $datadir;
+        # Copy datadir from installed system db
+        my $path= ($opt_parallel == 1) ? "$opt_vardir" : "$opt_vardir/..";
+        my $install_db= "$path/install.db";
+        copytree($install_db, $datadir) if -d $install_db;
+        mtr_error("Failed to copy system db to '$datadir'")
+          unless -d $datadir;
       }
     }
     else