I3S enviroment variable token

[aalexmonteiro]

Description

Implementation of improvements in i3s configuration, removing I3S_TOKEN, because is unncessary and updating the README and adjustig the creation of the i3s client to use ONEVIEWSDK_TOKEN when using the enviroment variable.

Issues Resolved

#183

Check List

• New functionality includes testing.
  • All tests pass ($ rake test).
• New functionality has been documented in the README if applicable.
  • New functionality has been thoroughly documented in the examples (please include helpful comments).
• Changes are documented in the CHANGELOG.

[jsmartt]

Looks good to me. I think eventually I'd like to see the I3S client be able to create a oneview client and take it's token automatically, effectively making the following work:

ENV['ONEVIEWSDK_URL'] = 'https://ov.example.com'
ENV['ONEVIEWSDK_USER'] = 'Admin'
ENV['ONEVIEWSDK_PASSWORD'] = 'secret123'
ENV['I3S_URL'] = 'https://i3s.example.com'

i3s_client = OneviewSDK::ImageStreamer::Client.new
# Note that I didn't have to set ENV['ONEVIEWSDK_TOKEN']

This will be helpful if we ever end up adding support for I3S endpoints in the cli.
But we can add that functionality in the future if we want.