bump pip version range

[wwwtyro]

It looks like something was pulling in pip 8.1.1 before we get to handling the wheelhouse, causing the attempted install of pip 7.1.2 to fail:

unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40 Processing ./wheelhouse/pip-7.1.2.tar.gz
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40 Exception:
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40 Traceback (most recent call last):
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40   File "/usr/lib/python3/dist-packages/pip/req/req_install.py", line 1006, in check_if_exists
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40     self.satisfied_by = pkg_resources.get_distribution(str(no_marker))
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40   File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 535, in get_distribution
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40     dist = get_provider(dist)
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40   File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 415, in get_provider
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40     return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40   File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 695, in find
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40     raise VersionConflict(dist, req)
unit-openvim-controller-0: 2016-05-25 18:31:45 INFO unit.openvim-controller/0.install logger.go:40 pkg_resources.VersionConflict: (pip 8.1.1 (/usr/lib/python3/dist-packages), Requirement.parse('pip===7.1.2'))

[marcoceppi]

I don't think this belongs here, since Xenial is pip 8.1.1 I believe this was done for reasons that pip 8.0 does not work on trusty

[marcoceppi]

So, this is on a Xenial machine. I booted up a trusty machine and did a pip install -U pip to get 8.1.1 and everything seemed OK. For consistency bumping the range here seems appropriate.

[johnsca]

The only reason pip was added to the wheelhouse at all instead of just using the system version was that the trusty version didn't have full wheelhouse support. We could perhaps instead add some conditional logic on the series to only update pip on trusty where it's actually required? But that would probably require still bundling the pip dependency in the wheelhouse and then just somehow excluding it for non-trusty deployments.

[marcoceppi]

OTOH, Having the latest version of pip on trusty wouldn't be a /bad/ thing, right?

[chuckbutler]

I don't think its a problem myself. I'd rather run tip of the runtime dependencies in charms myself (see: latest pip), however i'm sure there's another school of thought that disagrees with this logic (citation needed).

[johnsca]

I'm fine with this PR; I was just offering an alternative in case there was an issue with the newer pip on trusty.