Updates to pin charm-tools to 2.8.3

* Update requirements.txt to pin charm-tools to 2.8.3
* Update tox.ini to change the build parameters.
* This upgrades from <2.7 which adds reproducible charms
* Bug was fixed that controlled the default output directory
  doesn't get 'builds' appended.  The tox change puts it
  back so that stable & master both build to the same
  directory.  This may be reviewed in the future.

Change-Id: If175d58b7b663927d7e7be1c44550a9b8aaa5d79

requirements.txt

@@ -3,8 +3,24 @@
 # choices of *requirements.txt files for OpenStack Charms:
 #     https://github.com/openstack-charmers/release-tools
 #
+# NOTE(lourot): This might look like a duplication of test-requirements.txt but
+# some tox targets use only test-requirements.txt whereas charm-build uses only
+# requirements.txt
+setuptools<50.0.0  # https://github.com/pypa/setuptools/commit/04e3df22df840c6bb244e9b27bc56750c44b7c85
+
 # Build requirements
-charm-tools>=2.4.4,<2.8
-# importlib-resources 1.1.0 removed Python 3.5 support
-importlib-resources<1.1.0
+charm-tools==2.8.3
+
+# Workaround until https://github.com/juju/charm-tools/pull/589 gets
+# published
+keyring<21
+
 simplejson
+
+# Newer versions use keywords that didn't exist in python 3.5 yet (e.g.
+# "ModuleNotFoundError")
+# NOTE(lourot): This might look like a duplication of test-requirements.txt but
+# some tox targets use only test-requirements.txt whereas charm-build uses only
+# requirements.txt
+importlib-metadata<3.0.0; python_version < '3.6'
+importlib-resources<3.0.0; python_version < '3.6'

tox.ini

@@ -28,7 +28,7 @@ deps =
 [testenv:build]
 basepython = python3
 commands =
-    charm-build --log-level DEBUG -o {toxinidir}/build src {posargs}
+    charm-build --log-level DEBUG -o {toxinidir}/build/builds src {posargs}
 
 [testenv:py3]
 basepython = python3