libfs_avb: Fix unit test failures

There more output lines of `avbtool` now, adjusts the expected
output of `avbtool info_image --image test.img` in the test
cases.

Bug: 178215452
Test: atest libfs_avb_test
Test: atest libfs_avb_internal_test
Change-Id: I924d6d97ef0a4c19c93017c2491bf251dfc51cae