* `context/target` tests must be in groups 1 - 2.
* `context/controller` tests must be in groups 3 - 5.
This makes it easier to efficiently organize groups and balance test runtimes.
* config: singular ANSIBLE_COLLECTIONS_PATH
Every other *_PATH setting in ansible is singular, and the traditional
$PATH variable is also singular despite containing a list of
directories. Let's be consistent both internally and with POSIX
tradition.
* update all ANSIBLE_COLLECTIONS_PATHS env references to be singular
* deprecate plural ANSIBLE_COLLECTIONS_PATHS setting
