Updated openstack/openstack
Project: openstack/ceilometer  3b9ec825290ffbccd70ce914e1d14bc3760d2d59

basestring replaced with six.string_types

That's needed to move further in py3 compatibility.

Partially-Implements: blueprint ceilometer-py33-support
Change-Id: I5796de3b3f359c95ddc059374e19f7e7154e45c6