use fog 1.21

Allows us to stop holding credentials in the .fog file
Updating README to reflect new way to submit credentials.

With fog 1.21.0 you can now log on externally and provide your vcloud
token to fog.
remove bundle exec examples from README

Its usage as a gem doesn't require them.
tool name fix in README
add link to fog to README
Merge pull request #2 from alphagov/use_fog_1_21

Use fog 1.21.0 via vcloud-core 0.11.0