tests: add f_first_meta_bg_too_big test
The test verifies that e2fsck can properly fix a file system where the
value of s_first_meta_bg in the superblock is larger than the number
of block group descriptors in the file system. E2fsck will fix this
by clearing the meta_bg feature.
Signed-off-by: Theodore Ts'o <email@example.com>