libxfs: open-code "exit on buffer read failure" in upper level callers

libxfs: open-code "exit on buffer read failure" in upper level callers

Make all functions that use LIBXFS_EXIT_ON_FAILURE to abort on buffer
read errors implement that logic themselves.  This also removes places
where libxfs can abort the program with no warning.

Note that in libxfs_mount, the "!(flags & DEBUGGER)" code would
indirectly select LIBXFS_EXIT_ON_FAILURE, so we're replacing the hidden
library exit(1) with a null xfs_mount return, which should cause the
utilities to exit with an error.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>