Use tox in Makefile targets

Modify the Makefile to point at the appropriate tox targets
so that tox and Make output can be equivalent. This involves
mapping the lint target to the pep8 target and the test target
to the py27 target.

Add tox support to the charm.

Change-Id: I7c8078ebaac1bcfbc9993330127182ffe85a2220

requirements.txt

@@ -0,0 +1,11 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+PyYAML>=3.1.0
+simplejson>=2.2.0
+netifaces>=0.10.4
+netaddr>=0.7.12,!=0.7.16
+Jinja2>=2.6  # BSD License (3 clause)
+six>=1.9.0
+dnspython>=1.12.0
+psutil>=1.1.1,<2.0.0