changes in dependencies of dependencies of charm-tools have broken usage on trusty venvs

[ryan-beisner]

On Aug 16, this worked:

virtualenv .venv
. .venv/bin/activate
pip install charm-tools
charm version

charm unavailable
charm-tools 2.1.3

As of Aug 17, it doesn't:

virtualenv .venv
. .venv/bin/activate
pip install charm-tools
charm version

Traceback (most recent call last):
  File "/tmp/venv/bin/charm-version", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/tmp/venv/local/lib/python2.7/site-packages/pkg_resources.py", line 2720, in <module>
    parse_requirements(__requires__), Environment()
  File "/tmp/venv/local/lib/python2.7/site-packages/pkg_resources.py", line 592, in resolve
    raise VersionConflict(dist,req) # XXX put more info here
pkg_resources.VersionConflict: (setuptools 2.2 (/tmp/venv/lib/python2.7/site-packages), Requirement.parse('setuptools>=11.3'))

This appears to be because secretstorage revved up on Aug 17:
https://pypi.python.org/pypi/SecretStorage

And the reqs lineage goes like so:
cryptography->secretstorage->keyring->launchpadlib->charm-tools

Setting an upper constraint for secretstorage seems to resolve the issue:

virtualenv venv
. .venv/bin/activate
pip install 'secretstorage<2.3.0'
pip install charm-tools
charm version

charm unavailable
charm-tools 2.1.3

I am using: Trusty

Issue/Feature

I expect/expected the following

Charm-tools should successfully install in a virtualenv on Trusty.

What I got

Charm-tools has a dependency of a dependency that has changed, causing virtualenv charm-tools installations to break on Trusty.

[ryan-beisner]

Another way to look at this:

setuptools 2.2 is the default in a Trusty virtualenv.
setuptools 25.2.0 is the default in a Xenial virtualenv.

If setuptools is forced to >=11.3 (or ==25.2.0 as I just confirmed on a Trusty venv), this issue is also resolved.

[ryan-beisner]

FYI, the OSCI amulet test gate is currently blocked on this.

While it's possible to work around this by modifying the test-requirements.txt in all of the OpenStack Charms, charm-tools is the right place to fix it IMHO (secretstorage<2.3.0).