Allow out-of-source test runs

The test can now be run outside of the test source directory. Since the
`test_dir` global variable contains the absolute path to the test source,
all copying of configurations and execution of scripts can be done with
minimal changes.

maxscale-system-test/mdbci/run_test.sh

@@ -65,7 +65,8 @@ ulimit -c unlimited
 if [ $res == 0 ] ; then
     . ${script_dir}/set_env.sh $name
     cd ${script_dir}/..
-    cmake . -DBUILDNAME=$name -DCMAKE_BUILD_TYPE=Debug
+    mkdir build && cd build
+    cmake .. -DBUILDNAME=$name -DCMAKE_BUILD_TYPE=Debug
     make
 
     if [ ! -z "${named_test}" ] ; then

maxscale-system-test/mdbci/run_test_snapshot.sh

@@ -73,7 +73,9 @@ checkExitStatus $? "Error installing Maxscale" $snapshot_lock_file
 
 cd ${script_dir}/..
 
-cmake . -DBUILDNAME=$JOB_NAME-$BUILD_NUMBER-$target
+rm -rf build
+mkdir build && cd build
+cmake .. -DBUILDNAME=$JOB_NAME-$BUILD_NUMBER-$target
 make
 
 ./check_backend --restart-galera