Tag tasks update or install

* update tasks are meant to be the fast ones and the ones we want to be
  sure to always do (directory creations, permissions, etc.)
* install tasks are all the really slow things, like the git repo clone
  and package installations
* Every task can by run by --tags=install,update - which is the same as
  having no tags at all.

Conflicts:

	playbooks/roles/lms/tasks/main.yml
Merge pull request #65 from edx/feature/jrbl/tagging_update_install

Feature/jrbl/tagging update install