fsck: implement fsck -r {fd}

fsck: implement fsck -r {fd}

Make possible sending of statistics to a dedicated file descriptor.

Rationale: When UI is calling fsck from a remote terminal, fsck progress
needs to be sent to stdout. It is mixed there with output of statistics,
and it is impossible to parse the output to get the statistics.

Now it will be possible e. g. with "fsck -C -r 3 /dev/sda1"

Note: Code in if and else is intentionally partially duplicated. Current
human readable output of floats does not conform to locale conventions,
and may be changed in future. But we want to keep machine readable output
exactly same as it is now.

[kzak@redhat.com: - don't use report_stats_fd globally]

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
Signed-off-by: Karel Zak <kzak@redhat.com>