Fix python2.6 usage of unpack_from
Fix python2.6 usage of unpack_from

unpack_from in python 2.6 can't handle a bytearray.  Make it a buffer
before trying to unpack_from

Change-Id: I0b1014eba7b1001e79edb2bee1e1dc5b59eda36c

openstack/pyghmi,stackforge/pyghmi,benoit-canet/pyghmi,openstack/pyghmi