Update to charm-tools >= 2.0.0

The new release of charm-tools no longer ships the charm
command; update minimum version requirement and switch
to using charm-proof instead, unblocking current pep8
failures across all charms.

Also pin the version of requests to 2.6.0 until theblues
(indirect dependency of charm-tools) sort out its
requirements versioning.

Change-Id: Ifb8974dbd681d3117152a8f7a7bfc889d6c3f315

test-requirements.txt

@@ -3,5 +3,6 @@ coverage==3.7.1
 mock==1.0.1
 flake8==2.1.0
 # No version required
-charm-tools
+charm-tools>=2.0.0
 os-testr
+requests==2.6.0

tox.ini

@@ -21,7 +21,7 @@ basepython = python2.7
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = flake8 {posargs} hooks unit_tests tests
-           charm proof
+           charm-proof
 
 [testenv:venv]
 commands = {posargs}