oeqa/selftest/archiver: Add multiconfig test for shared recipes

Test that the shared recipes in original mode with diff enabled works in multiconfig,
otherwise it will not build when using the same TMP dir.

The test can be run with:

oe-selftest -r archiver.Archiver.test_archiver_multiconfig_shared_unpack_and_patch

| oe-selftest - INFO - test_archiver_multiconfig_shared_unpack_and_patch (archiver.Archiver)
| oe-selftest - INFO -  ... ok
| oe-selftest - INFO - ----------------------------------------------------------------------
| oe-selftest - INFO - Ran 1 test in 52.948s
| oe-selftest - INFO - OK
| oe-selftest - INFO - RESULTS:
| oe-selftest - INFO - RESULTS - archiver.Archiver.test_archiver_multiconfig_shared_unpack_and_patch: PASSED (49.98s)
| oe-selftest - INFO - SUMMARY:
| oe-selftest - INFO - oe-selftest () - Ran 1 test in 52.948s
| oe-selftest - INFO - oe-selftest - OK - All required tests passed (successes=1, skipped=0, failures=0, errors=0)

Signed-off-by: Jose Quaresma <jose.quaresma@foundries.io>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>