maxscale-system-test changed in order to control test environment by itself.
Every test checks which machines are running, compare with list of needed machines
and start new VMs is they are missing in the running machines list.
Tests are executiong MDBCI commands, MDBCI executable should be in the PATH
The paths were wrong in the scripts used to run tests. The same problem
was in the CMake files that used CMAKE_SOURCE_DIR instead of
CMAKE_CURRENT_SOURCE_DIR.
Added missing check for BUILD_SYSTEM_TESTS in avrorouter for the
workaround to building without all dependencies present.
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.
