Convert apt::key to use anchors

[reidmv]

Previously, apt::key used a noop exec hack to do exactly what anchors were intended to be used for. This commit removes the exec hack and achieves the same end using Anchor resources from the puppetlabs/stdlib module.

[reidmv]

In case it isn't clear what's going on here, I'm pasting some example puppet code and the resulting dependency graph to try and illustrate the cases that necessitate all this complicated looking anchor stuff. It's not completely self-explanatory but it might be somewhat helpful.

Code

apt::source { "ubuntu_partner":
  include_src => true,
  location    => "http://archive.canonical.com/ubuntu",
  key         => "437D05B5",
  key_server  => "pgp.mit.edu",
  repos       => "partner",
}

apt::source { "ubuntu_mirror_wsu":
  location    => "http://ubuntu-releases.eecs.wsu.edu",
  key         => "437D05B5",
  key_server  => "keyserver.ubuntu.com",
  repos       => "main restricted universe multiverse",
}

apt::source { "ubuntu_mirror_psu":
  location    => "http://mirrors.cat.pdx.edu/ubuntu",
  key         => "437D05B5",
  key_server  => "pgp.mit.edu",
  repos       => "main restricted universe multiverse",
}

apt::source { "cat_internal_repo":
  location    => "http://mirrors.cat.pdx.edu/cat",
  key         => "1EE15D43",
  key_server  => "pgp.mit.edu",
  repos       => "main",
} 

Resulting Dependency Graph

Full size image