Fix out-of-source runs of mxs791_galera.sh

The test used the current directory instead of the source directory where
the script was located.

maxscale-system-test/mxs791_galera.sh

@@ -4,14 +4,14 @@
 ## @file mxs791.sh Simple connect test in bash
 ## - connects to Maxscale, checks that defined in cmd line DB is selected
 
-rp=`realpath $0`
+srcdir=$(dirname $(realpath $0))
 export test_dir=`pwd`
 export test_name="mxs791_galera.sh"
 echo test name is $test_name
 
-$test_dir/mxs791_base.sh
+$srcdir/mxs791_base.sh
 
 res=$?
 
-$test_dir/copy_logs.sh $test_name
+$srcdir/copy_logs.sh $test_name
 exit $res