Merge lp://staging/~sinzui/charms/precise/elasticsearch/exec-d-support into lp://staging/~charming-devs/charms/precise/elasticsearch/trunk

Update the charm to use templates and support exec.d for private clouds.

Update the charm to use templates and support exec.d for private clouds.

RULES

    For Webops (mthaddon)
    * Add an exec.d clause to allow webops to prepare the charm canonistack.
    * Use cheetah to create elasticsearch.yml template.

    ADDENDUM
    * OMG! config is broken. While I lost the cluster-name when I updated
      the charm to use apt, I find some small comfort that the config
      could only be written once. Subsequent changes were either
      ignored or error-ed.
      * Always regenerate elasticsearch.yml when the config changes.
    * The local plugin is ignored because the url has three-slashes in it:
      file:/// which I think is correct, but
      file:///var/ is changed to file:/var by the plugin installer, but it
      does like file://var

IMPLEMENTATION:

I added the exec.d hook. The script fails over to the PPA I setup.
    hooks/install

I extracted the AWS template (that webops will not use). I then moved the
rules to generate the yml to common.sh so that it can be called from both
install and config-changed.
    templates/
    templates/elasticsearch.yml.tmpl
    hooks/common.sh
    hooks/config-changed
    hooks/install

Remove the extra slash to make bin/plugin happy.
    hooks/install

Incremented the charm and removed config vars that are never used.
    revision
    config.yaml