Bug 1877: Artifactory times out

Added a lockable resource semaphore around queries to artifactory
to prevent overloading the server.

Fixes Bug 1877

Change-Id: I17979e7fa5d2ed2405873e7dda588d7104741817
Signed-off-by: beierlm <mark.beierl@canonical.com>
(cherry picked from commit f83c20ab)