Support for Python 2.6 dropped in the OpenStack backend

[Riccardo Murri]

Hi *,

I've just committed a change to the "master" code which removes
support for Python 2.6, limited to the OpenStack backend. In short,
if you try to use GC3Pie with Python 2.6, installation will work but
the OpenStack resources will *not* be created.

Here is the commit message, which gives a bit more details:

"""
Upstream has ceased supporting Python 2.6 since `novaclient` version 3.0.0; at
the time of this writing, we're past 7.0 already and it's really become
impossible to keep code compatible across so many major revisions. Since we're
dropping support for Python 2.6 in GC3Pie soon-ish, start by ceasing support for
the OpenStack backend on Python 2.6.

Installation of the optional feature `[openstack]` will *not* error out (which
could be regarded as a bug, but I could not figure out how to detect when it's
being installed from within `setup.py` and return a meaningful error message),
but any attempt to use an `OpenStackLrms` resource will result in a
`ImportError` (which automatically disables the resource).
"""

Ciao,
R