Make more tests run in a remote cluster

[hhorak]

PR #308 added a test that can run in both, local and remote cluster. It would be nice to change the rest of the tests from local cluster test suite to allow them run on remote cluster as well and move to the common file with test functions.

[pkubatrh]

@phracek to take a look

[phracek]

Nowadays we have these three tests:

test_postgresql_integration
test_postgresql_imagestream
run_latest_imagestreams_test