phase1: reduce verbosity of rsync

phase1: reduce verbosity of rsync

The purpose of this patch is to reduce uplink bandwidth contention when
rsync uploads are running.

This patch:
- replaces '-v' and '--progress' by '--info=name' in rsync's parameter
  list (assuming it's necessary to output a list of updated files)
- introduces a wrapper script 'rsync.sh' which checks for the presence
  and executability of 'pv' and pipes the output of rsync through
  'pv -t -i 60 -f' if possible, and falls back to plain rsync otherwise.

'--info=name' prints one line to stdout for each file that is updated on
the remote side.
'pv -t -i 60 -f' prints a 1mn-resolution timer to stderr, with the goal
of preventing the current buildbot step to timeout due to lack of process
output.

It's worth noting that '--progress' did not prevent some timeouts (most
notably on the 'sourceupload' step) since --progress only emits output
for files that are updated on the remote side.

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>