Merge lp://staging/~chad.smith/charms/precise/block-storage-broker/bsb-ec2-boto into lp://staging/charms/block-storage-broker

This branch moves block-storage-broker's EC2-specific methods from euca2ools to AWS' python SDK (python-boto).

The reason for this change is to avoid significant incompatibilities in euca2ools libraries that have been introduced across euca2ools major releases. By consuming python-boto instead of internal euca2ools libraries, we access a more stable API supported by Amazon that will remain more stable across releases than internal euca libs. As written this code currently also has been tested on trusty and will be used as well as the trusty release of this charm.

This can be quickly tested on AWS either using precise or trusty by changing the postgresql-storage-bundle.cfg:
  - change all mention of precise to trusty
  - change postgresql-9.1-debversion to postgresql-9.3.debversion

Test procedure is something like the following:

1. Create postgresql-storage-bundle.cfg as exemplified below, replacing the EC2_* values with valid credentials and endpoints.

2. juju-bootstrap -e your-ec2-environment
# to deploy block-storage-broker, storage subordinate and postgresql and create and attach a volume.
3. juju-deployer -c postgresql-storage-bundle.cfg doit-no-volume

----- postgresql-storage-bundle.cfg -----
common:
    services:
        postgresql:
            branch: lp:~charmers/charms/precise/postgresql/trunk
            constraints: mem=2048
            options:
                extra-packages: python-apt postgresql-contrib postgresql-9.1-debversion
                max_connections: 500
        block-storage-broker:
            branch: lp:~chad.smith/charms/precise/block-storage-broker/bsb-ec2-boto
            options:
                provider: ec2
                key: <your EC2_ACCESS_KEY>
                endpoint: <your EC2_URL>
                secret: <your EC2_SECRET_KEY>

doit-no-volume:
    inherits: common
    series: precise
    services:
        storage:
            branch: lp:~charmers/charms/precise/storage/trunk
            options:
                provider: block-storage-broker
                volume_size: 9
    relations:
        - [postgresql, storage]
        - [storage, block-storage-broker]

doit-with-volume-map:
    inherits: common
    series: precise
    services:
        storage:
            branch: lp:~charmers/charms/precise/storage/trunk
            options:
                provider: block-storage-broker
                volume_size: 9
                volume_map: "{postgresql/0: YOUR-EXISTING-EUCA-VOLUME-ID}"

    relations:
        - [postgresql, storage]
        - [storage, block-storage-broker]