If QUBES_TEST_TEMPLATES or QUBES_TEST_LOAD_ALL is set, create testcases
on modules import, instead of waiting until `load_tests` is called.
The `QUBES_TEST_TEMPLATES` doesn't require `qubes.xml` access, so it
should be safe to do regardless of the environment. The
`QUBES_TEST_LOAD_ALL` force loading tests (and reading `qubes.xml`)
regardless.
This is useful for test runners not supporting load_tests protocol. Or
with limited support - for example both default `unittest` runner and
`nose2` can either use load_tests protocol _or_ select individual tests.
Setting any of those variable allow to run a single test with those
runners.
With this feature used together load_tests protocol, tests could be
registered twice. Avoid this by not listing already defined test classes
in create_testcases_for_templates (according to load_tests protocol,
those should already be registered).
Test base functions of dom0 module (creating VM, setting property) and
configuring system inside of VM (through DispVM). The later is done for
each available template (the process use salt installed in that
template, not copied from dom0).
QubesOS/qubes-issues#3316
