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/testconnections.cpp

@@ -88,7 +88,6 @@ TestConnections::TestConnections(int argc, char *argv[]):
 #ifdef SIGBUS
     signal_set(SIGBUS, sigfatal_handler);
 #endif
-    chdir(test_dir);
     gettimeofday(&start_time, NULL);
 
     read_env();