Add option to use single minicluster for a group of tests to improve run time.

[minaevd]

Currently a minicluster is created for every single test and it takes too long and sometimes can be unnecessary. This option can be used to improve run time of running multiple tests by setting up a single minicluster instead for all the tests in suite.

[lofifnc]

This is a duplicate of #25. However as there is concrete interest in this feature, I'm going to look into this next.