gsyncd / geo-rep: Introduce basic crawl instrumentation

This patch extends the persistent instrumentation work done by
Aravinda (@avishwa), by introducing a handfull of instrumentation
variables for crawl. These variables are "pulled up" by glusterd
in the event of a geo-replication status cli command and looks
something like below:

"Uptime=00:21:10;FilesSyned=2982;FilesPending=0;BytesPending=0;DeletesPending=0;"

"FilesPending", "BytesPending" and "DeletesPending" are short-lived
variables that are non-zero when a changelog is being processes (ie.
when an active sync in ongoing). After a successfull changelog process
"FilesPending" is summed up into "FilesSynced". The three short-lived
variabled are then reset to zero and the data is persisted

Additionally this patch also reverts some of the changes made for
BZ #986929 (those were not needed).

Change-Id: I948f1a0884ca71bc5e5bcfdc017d16c8c54fc30b
BUG: 990420
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/5441
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>