Add integration test that inspects and builds a SCC registered system.

Inspect a SLES12 SCC registered system and build a new image using the
inspected data.
Make :slow tagged integration tests not run with a default rspec run.

Some tests are quite slow due to build steps. To not run all of those on local
developer machines but only on the CI server we introduce a :slow tag and
make execution of slow_tests optional.
Merge pull request #277 from SUSE/review_141009_add_integration_test_for_scc_registered_sles12

[Review] Request from 'greygoo' @ 'SUSE/machinery/review_141009_add_integration_test_for_scc_registered_sles12'