Add root_helper param to get_connector_properties

This patch adds the ability to pass in a custom
root_helper for executing commands.  This is needed
for other projects that need a custom root-wrapper,
such as nova.

fixes Bug #1213135

Change-Id: Ie18276ae2e736bb2276d4e9c57385d2588441428
Merge "Add root_helper param to get_connector_properties"