Use a fixed and rbh-specific value for FID length.

This prevents compatibility from suddenly breaking if the
lustre FID length value changes. Added a compile-time check
to make sure that the value remains consistent.
Disable scan timeout by default (dangerous feature that can lead to threads deadlock).
Small code cleaning in lmgr_report.
migration: better management of pending migration volume.

Pending migration volume was not accurate enough and resulted
in slow migration (file per file) when the size limit was closed
to be reached.
This patch distinguish in enqueued volume the amount of data that
was supposed to be copied, but was finally not (VOL_NOK).
Thus the pending volume can be computed as:
vol_sumitted - VOL_OK - VOL_NOK.
pipeline: fixed regression introduced by e214f1f1.

Most file attributes where not updated when performing an update scan,
or even when processing changelogs...
tests: added clear message why test 300 fails.
rbh-config: completed changelog mask with missing interesting records.
packaging: set distrib version to 2.5.0-alpha1
packaging: dependency to libmysqlclient is automatically set by rpmbuild.

libmysqlclient_r.so is not always installed in the system
(only libmysqlclient_r.so.<major> may be present).
It's better to let rpmbuild add the dependency rule in the RPM
based on ldd return on the binaries.