testimage: add ability to export tests

testimage: add ability to export tests

Add the ability to export the tests so that they can run independently of
the build system, as is required if you want to be able to hand the test
execution off to a scheduler.
Booting/deployment of the target is still handled by the build system,
as before, only the execution of the tests happens outside of the build system.
Tests exported are the ones defined in TEST_SUITES.

No tests have been changed as interesting parts of the data store have been
exported and tests can continue to query them as before. Small adjustments were made
for a couple of oeqa modules though.

[YOCTO #5613]

(From OE-Core rev: 155dd52e0f707e06f50756584a50f744ba6b7844)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>