Updated version requirement for pyghmi

This patch updated the pyghmi version from 0.5.8 to 0.6.11.
pyghmi is required by ironic. The newer version of pyghmi
has serial console support as well as some bug fixes that
are required by ironic.

Change-Id: I11f60bf7d38def0ba7686c89890e262c155c703c
Merge "Updated version requirement for pyghmi"