Git: Better support for multiple repositories

[flosell]

Some use cases demand that more than one repository can be checked out into the same workspace.
At the moment, git support is very specific on only supporting one directory.

As a workaround, you can obviously use shell commands to check out repositories into a workspace yourself.

Maybe this could be tied in with the general purpose workspace to be implemented in #72 to create a composable, flexible solution, maybe something like this:

(with-workspace
  checkout-foo
  checkout-bar
  do-something)

[flosell]

with-workspace was implemented in #72, and the new lambdacd-git library will have a separate cloning step along these lines:

(defn clone-foo [args ctx]
  (lambdacd-git/clone ctx foo-repo "master" (str (:cwd args) "/foo")))

(defn clone-bar [args ctx]
  (lambdacd-git/clone ctx bar-repo "master" (str (:cwd args) "/bar")))

(with-workspace
  clone-foo
  clone-bar
  do-something)

Follow flosell/lambdacd-git#2 for updates