e2fsck: Skip journal checks if the fs is mounted and doesn't need recovery

e2fsck: Skip journal checks if the fs is mounted and doesn't need recovery

If we are checking a mounted filesystem (typically the root
filesystem, mounted read/only) and the NEEDS_RECOVERY flag is not set,
skip all of the checks associated with making sure the journal is
consistent.  There is the very slight possibility we could lose if the
NEEDS_RECOVERY flag was somehow cleared even though there was data in
the journal, but this has practically never happend in practice, and
it reduces the number of reads required at boot-time, which is a big
deal when trying to reduce boot times with HDD's.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>