test_build: Add simple sanity check for explicit erase (-E)

Change-Id: I210bd45431d2fa67118ab357df1b946bc83a3235
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/74323
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed