deploy: created git deployer
deploy: removed deploy.go file

provisioner: adding Deploy method to provision.

We're are going to implement the Deployer as a single Deploy function,
so the interfaces in that file where removed. The provisioner now is
responsible to implement a Deploy method, which follows the definition
of the interface that was present here.
deploy: created git deploy

Also refactoring the deploy function (moved from juju provisioner).
provision/docker/provisioner,testing/provisioner: using provision.App instead of dead deploy.App interface
provision/juju,provision/lxc: using deploy.Git function

Since the deploy process is the same for both, juju and lxc
provisioners, we're now sharing the git deploy process using the deploy
pkg.