feat(contrib/coreos): add etcd debug unit

This adds an optional service to aid in debugging etcd issues.
Note that it's only enabled in the cloud-config file, not started.
This enables users to `sudo systemctl start debug-etcd` on a machine
before performing tasks which may strain etcd (such as heavy IO),
and then watch the service's journal to see how things like heartbeat
intervals change.
docs(troubleshooting_deis): document debug-etcd service
docs(releases): update with major/minor and patch procedures
feat(contrib/ec2): use separate volume for /var/lib/docker

We've seen fewer performance issues when machines use a separate
volume for /var/lib/docker. This commit changes the AWS provision
script to automatically prepare and mount a separate volume for
Docker.

We have to touch `/etc/docker-volume-formatted` because the
user-data is applied on every reboot, and we don't want
the Docker graph getting destroyed.

Note that we use the device name `/dev/xvdf` irrespective
of the instance virtualization type (PV or HVM). This seems to be
the way the kernel maps the block device, and isn't necessarily
unusual - see http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-using-volumes.html

Amazon documentation suggests using the letter 'f' as the first name
of a non-root EBS-backed device: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html

I manually tested this on both PV and HVM instances and had no issues.
There is no change in UX other than the new requirement of installing
the PyYAML Python library.
ref(controller): remove redis cache library and settings

CACHE_URL and the python Redis library were not actually being
used by the controller.
chore(controller): update South to 1.0.2 bugfix release
chore(cache): update Redis to 2.8.19

See https://raw.githubusercontent.com/antirez/redis/2.8/00-RELEASENOTES
fix(client): encode unicode properly for apps:run
Merge pull request #2779 from carmstrong/feat-debug_etcd

feat(contrib/coreos): add etcd debug unit
Merge pull request #2800 from mboersma/update-rel-docs

docs(releases): update with major/minor and patch procedures
feat(contrib/ec2): use absolute path names for scripts

This enables users to run the AWS provision script from any directory.
Merge pull request #2804 from mboersma/remove-redis-py

ref(controller): remove redis cache library and settings
Merge pull request #2814 from mboersma/update-south

chore(controller): update South to 1.0.2 minor bugfix release
Merge pull request #2815 from mboersma/update-redis

chore(cache): update Redis to 2.8.19
Merge pull request #2813 from mboersma/fix-cli-unicode

fix(client): encode unicode properly for apps:run
Merge pull request #2803 from carmstrong/ec2-docker_volume

feat(contrib/ec2): use separate volume for /var/lib/docker
ref(controller): remove several unused settings

The ACCOUNT_* settings were not removed when django-allauth was,
and DEFAULT_BUILD is not referenced anywhere.
ref(controller): remove redundant ALLOWED_HOSTS setting
Merge pull request #2817 from mboersma/controller-cruft

Remove controller settings cruft