commit 2789f144d4 uses service.py
in openstack-common and changes the collector from a manager into
a Service. The rpc connection creation in CollectorManager is not
called any more. So, remove the unnecessary rpc import.
Change-Id: I710e14beb3485661e8aeeae0792fae68cba48979
Signed-off-by: Shane Wang <shane.wang@intel.com>