Update OpenStack driver to map more node states to states recognized by
Libcloud.

Patch by Chris DeRamus.
Add support for HTTP proxy to LibcloudHTTPConnection and
LibcloudHTTPSConnection class.

User can specify which HTTP proxy to use using one of the following
approaches:

* by setting "proxy_url" environment variable (global / process wide)
* by passing "proxy_url"  argument to the Connection class constructor (per
  connection instance)
* by calling "set_http_proxy" method on the Connection class (per connection
  instance)
Update CHANGES.
Fix broken test and invalid variable declarations.
Allow user to pass proxy_url argument to Connection class.
Add missing variable assignment.
Fix a typo in the example.
Add new base paused node state.
Update Node.__repr__ to display a friendly name for the state attribute.
Update HTTP proxy code so it supports basic auth authentication.
Update cURL lines to include proxy basic auth information (if available).
Update proxy support so it also works with Python 2.6.
Add missing "set_http_proxy" method to the base Connection class
Improve URL validation, update docstring.
Fix a typo.

Spotted by Brian Johnson.
update linode plans mapping

Closes #351

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
[LIBCLOUD-544] Fix the regression caused by the original implementation of the bugfix. We now perform a simple sanity check to know whether the metadata dictionary has already been formatted to GCE's specs.
Remove my own tests before pushing, whoops.
Add a meaningful error message when malformed
metadata field is provided.
Improve code readability