mkfs: factor boolean option parsing

mkfs: factor boolean option parsing

Many of the options passed to mkfs have boolean options (0 or 1) and
all hand roll the same code and validity checks. Factor these out
into a common function.

Note that the lazy-count option is now changed to match other
booleans in that if you don't specify a value, it reverts to the
default value (on) rather than throwing an error.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jan Tulak <jtulak@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>