Use OSError instead of ProcessExecutionError.
Use OSError instead of ProcessExecutionError.

This patch updates the ZeroMQ test module to use OSError in one place
instead of ProcessExecutionError from nova.exception.  In a previous rev
of this code, it was using nova.utils.execute(), but no longer does.

Change-Id: I3dac2981b5c1a7cd5fc0e4e8dbf0a2d378a1d136

n0ano/gantt,n0ano/gantt