use -f with pgrep

pgrep will not be able to get th pid using the full path which is $libexec/mysqld unless -f is being used

support-files/mysql.server.sh

@@ -386,7 +386,7 @@ case "$mode" in
       fi
     else
       # Try to find appropriate mysqld process
-      mysqld_pid=`pgrep $libexecdir/mysqld`
+      mysqld_pid=`pgrep -f $libexecdir/mysqld`
 
       # test if multiple pids exist
       pid_count=`echo $mysqld_pid | wc -w`