ci(signer-id): add a test case for signer-id

Added a test to verify that the signer-id of the images is not zero.
Signer-id is a hash of the key that eventually passes down to RSS, along
with the measurement of the image that this key signs.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ibd8f2eda2570c9ba7f1fbe22b643cf46e569d205
4 files changed