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)