Rename 'plugintestutils' package to 'testing'
Following discussion on #buildstream, it seems to be agreed that the name plugintestutils is a bit of a mouthfull, and that testing is a better name for this package. If we're going to rename it, we should do it sooner rather than later.
So far, as far as I can tell, plugintestutils is only being used by bst-plugins-container, bst-plugins-template and one other user.
both bst-plugins-container, bst-plugins-template use buildstream master in their CI so I'll open paralell MR's to those and link them below.
Changes proposed in this merge request:
- Rename 'plugintestutils' package to 'testing'
- Disable the external tests against bst-plugins-template. This will fail as those tests are still importing buildstream.plugintestutils. This will need to be reenabled once bst-plugins-template has been patched.