test: correct time stamps for UEFI authentication

A time authenticated variable cannot be overwritten with another value
with the same time stamp. So we must ensure the correct sequence of time
stamps when generating out test data.

Using parameter -t for sign-efi-sig-list gives reproducible results and
avoids sleep statements.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>