testimage: Support full TC path such oeqa.runtime.pnp.get_memory_size in TEST_SUITES

testimage: Support full TC path such oeqa.runtime.pnp.get_memory_size in TEST_SUITES

If a TC name start with "oeqa", it is thought as a full TC path. if not,
follow original logic (assume under oeqa.runtime)

For example:

TEST_SUITES = "oeqa.runtime.pnp.get_memory_size oeqa.runtime.sanity.reboot"

will run these two case when bitbake -c testimage

[YOCTO #7834]

Signed-off-by: zjh <junhuix.zhang@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>