If this play is being run against an existing mmapv1 mongo 3.0 install,
make sure MONGO_STORAGE_ENGINE is overridden.

This will facilitate shipping 3.0 with newer release.

This allows for security updates to be applied during artifact creation,
but not applying other updates.

ECOM-6141

Added new setting variable "EXPIRING_SOON_WINDOW: 28"

This method relied on the `hostvars` variable provided by ansible to always
be all the nodes in the rabbitmq cluster.  The hostvars var broke as a result
of the upgrade to ansible 1.9 but also even if it did work, this method
required that you always run rabbit plays on the whole cluster.  This is not
reasonable as it makes it very hard to heal a single node that may have fallen
over.

From here on, the RABBITMQ_CLUSTERED_HOSTS var should be used instead to
specify the rabbit hosts that are part of a cluster.

ECOM-2618

Removed post.txt from the list of files that will have its github urls replaced with git mirror urls.

Having `--tags deploy` be part of the ansible-playbook call
that `/edx/bin/update` makes is not intuitive.  It's broken
us a few times recently and I don't think the benefit it
provides is worth the cost and confusion.  I feel that anyone
who wants to use tags will know how to do it without using
`/edx/bin/update`.

Setting a default value and adding a changelog entry.

Changed the incorrect case of mongo_clustered to MONGO_CLUSTERED
that broke cluster configuration.