Added few tests to contentviews related to publishing

Tests covered

1) promote_custom_content
2) publish_version_changes_in_target_env
3) publish_version_changes_in_source_env

I had tried moving the common code for target_env and source_env  to a function, but things were getting too complex.

Also my personal feeling is there are too many assert statements for 2) and 3), but felt needed to avoid false positives. Let me know if any changes are desired.