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
If a MaxScale-generated configuration defines an empty value, it is
ignored with the assumption that the next modification will cause the
problem to correct itself.
Added some helper functions into the MaxScale class and default parameters
into the connection creation functions. Also made the ip() function const
correct.
