Add better coverage support under tox

For those in the community who don't use run_tests.sh but want
tox to have coverage support this small change should help.  It
adds coverage erase, combine, html reporting.  It also
fixes the coverage unit tests in two ways.  The first is
adding the locking like normal unit tests. The second
is adding substring regular expression matching to pick
a subset of tests.  This brings it up to closer par with
run_tests.sh.

Change-Id: If9ea229425dc9a191fa7c5cc073cf5da412a69b7
Support detection of fixed ip already in use

Update the validate_networks method to detect when a fixed ip is
already in use and raise the FixedIpAlreadyInUse exception

Change-Id: I07f83ce654c909b1158315dfc21a40654bc34a47
Closes-Bug: #1247844
Add development policies section to devref

We now have a whole bunch of unwritten development policies about what is
allowed and what isn't, it is time to write some of them down.

A subsequent patch will add the first policy.

Change-Id: I91c2eb2b937f38b3b3c5380ac93fa0ce0f5e4156
Add out of tree support dev policy

Record what our policy is around supporting out of tree code.

Change-Id: I718ef7f0b6c29a85be89292d051f07b4cdd32676
Fix a wrong comment in the code

The docstring in the ExtensionManager class indicates a test file as
guide file, but the path reported is wrong.

Change-Id: I1b95d591cee6da3cc760c365c88ae1809973b98c
websocketproxy: remove leftover debug output

Someone reported the following very long entry in their
/var/log/messages:

  Jun  6 15:00:16 gprfc041 nova-novncproxy: }}>>{<{<}>{<{<}> [...]

It turns out that this is from some debug code left in this module.
Just drop it.

Change-Id: I392f599e81790376dab11f9323430ee9abcff444
Merge "Fix a wrong comment in the code"
Merge "Add better coverage support under tox"
Merge "Support detection of fixed ip already in use"
Merge "Add development policies section to devref"
Merge "Add out of tree support dev policy"
Merge "websocketproxy: remove leftover debug output"