Add storage scripts

[Duncan McGreggor]

In bug #482357, Robert Collins suggested that we start adding command line tools for txAWS. A blueprint has been opened for this here:
  https://blueprints.edge.launchpad.net/txaws/+spec/scripts-for-txaws

This ticket addresses the need for adding scripts for the txaws.storage functionality.

Note from the blueprint that we want to provide compatibility with ec2-api-tools and eucatools as much as possible.

This branch needs to take into consideration the following:
 * how ec2-api-tools and euca-tools use environment variables and files
 * compatibility of command line options (with the aforementioned tools)
 * the naming of scripts in the ./bin directory (txaws-*, and named like ec2-api-tools)
 * the creation of a txaws/scripts/ subpackage

Here is a list of the currently supported S3 calls in txAWS, and thus the scripts that will likely be needed for this branch:
 * txaws-list-buckets
 * txaws-create-bucket
 * txaws-delete-bucket
 * txaws-put-object
 * txaws-get-object
 * txaws-head-object
 * txaws-delete-object

[Duncan McGreggor (oubiwann)]

Setting credentials in Euca2ools:

EC2_URL -U or --url [url] http://host:8773/services/Eucalyptus
or http://ec2.amazonaws.com
or https://ec2.amazonaws.com:443

S3_URL -U or --url [url] http://host:8773/services/Walrus
or http://s3.amazonaws.com
or https://s3.amazonaws.com:443

EC2_ACCESS_KEY -a or --access-key [key] Access Key ID / Query ID
EC2_SECRET_KEY -s or --secret-key [key] Secret Access Key / Secret Key
EC2_CERT -c or --cert [file] user's PEM-encoded certificate
EC2_PRIVATE_KEY -k or --privatekey [file] user's PEM-encoded private key
EUCALYPTUS_CERT --ec2cert_path [file] OPTIONAL path to cloud cert

[Duncan McGreggor (oubiwann)]

Note that several ticket have been created for future work as a result of working on this one.

[Duncan McGreggor (oubiwann)]

  Merged 484858-s3-scripts [r=lifeless] [f=484858]

  This change starts the beginning of script support in txAWS, the first scripts
  being for the s3 API.