Flush out the remainder of test_link.py

[schwehr]

Things todo and questions to answer from working on #211

• ~Does class Link need an __eq__? And the same for many of the other classes. The default behavior isn't very useful~ - Moved to #222
• test_minimal: Cannot call link.get_href() after set_owner. Got an error
• test_minimal: Test link.resolve_stac_object()
• Test get_href when href is absolute and there is an owner
• Test get_absolute_href when there is an owner
• Test when resolve_stac_object on link when target is a str.

[duckontheweb]

Moving this out of the 1.4.0 release since it does not seem critical

[jsignell]

It is a little hard to map these back to the current state of the tests, but I am fairly confident that all the cases listed in the original description are captured in the tests at this point.

This is probably fine to close.

[gadomski]

Yeah, I think so too. There are some slightly worrying misses in the link.py coverage but I don't think any of the suggested fixes in this issue touch those. Closing as done.