Fix ESP detection

1. adjust the regular expression to meet correct ESP which partition
   index greater than 10.
2. output the right failure filename in deferred_check_uefi_logs_esp()

Signed-off-by: Weizhao Ouyang <weizhao.ouyang@arm.com>
[Backport commit 42f6bc3c.]
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>