It's of no guarantee that core plugin implements counter/getter function
for a CountableResource. Instead of just trying core plugin, try every
plugin registered in the directory.
To retain backwards compatibility, we also make sure that core plugin is
checked first.
Change-Id: I5245e217e1f44281f85febbdfaf873321253dc5d
Closes-Bug: #1714769
(cherry picked from commit 07bfe6adb9)