fsck: Add a -r option to report memory and runtime statistics

fsck: Add a -r option to report memory and runtime statistics

This patch adds a "-r" option to report statistics for each fsck run.
It gathers the statistics via wait4() and rusage and reports exit
status, system and user CPU time, elapsed wall-clock time and the max
RSS.

[kzak@redhat.com: - rebase to the latest code,
                  - report all on one line,
                  - use "real" rather than "elapsed"]

Signed-off-by: Frank Mayhar <fmayhar@google.com>
Signed-off-by: Karel Zak <kzak@redhat.com>