Switching to juju-mongodb

[Curtis Hovey-Canonical]

I want to start testing the packaging rules to include juju-mongodb
with juju-local. Reading the code in provider local, I believe juju
will fail because it requires mongodb-server. It will install it for
trusty.

How do we want to solve this? Juju could see that the version is
trusty or newer and choose to install juju-mongodb. We might consider
a metapackage that juju installs, and we create the packages to know
which mongodb to get.

Do we need an switch env option to choose which mongodb we need during
the testing transition?

-- 
Curtis Hovey
Canonical Cloud Development and Operations
http://launchpad.net/~sinzui