oeqa/{core,selftest}: Add support to validate if a specified test case isn't found
If some test module/case is specified to run and isn't found the OEQA
framework didn't notice it, so complete the implementation using
modules_required and validate for the test case prescense.
Raise an exception when the test module/case required isn't found.
[YOCTO #11645]
Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
