This patch makes sure that we have only one job instance (see bug 313153
for reason) and that all folders scheduled to refresh are processed even
if an exception happens while refreshing one of them.

Change-Id: I4fc93e84dc33ac42749e8ebe4e399c502d44f188
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>