Remove default root_helper of sudo for remotefs

This patch removes the default root_helper of sudo
for the RemoteFsClient.  We should be using the
cinder.utils.get_root_helper()

Fixes Bug #1223879

Change-Id: I8ba61cd6ac09b85b9ca924a9cf43c2dcea8e6c15
Merge "Remove default root_helper of sudo for remotefs"