rtstool on Ubuntu installs in /usr/local/bin

rtstool on Ubuntu installs in /usr/local/bin

The cinder-rtstool which is required to use LIO iscsi_helper
installs in /usr/local/bin on Ubuntu and /usr/bin on RHEL
variants.  Currently the rootwrap.conf only has /usr/bin
configured, as a result LIO can't be used on Ubuntu without
modifying the rootwrap file.

This patch just adds /usr/local/bin to the rootwrap.conf; Honestly
I'm not sure if this is good, bad or doesn't matter.  May be able
to address this via documentation, or upstream in the packaging of
cinder-rtstool instead?  Not sure what's preferred.

Change-Id: I577e10df25181c7d4ca8189b10640a8e6e39b047
Closes-Bug: #1402076