Fixes testCreateAndRunAService by fixing the outdated jetty URL
JCLOUDS-127: Added a method to check if the context is open

- Added isOpen in Context interface
- Refactoring Closer class:
  - method close can only call once
  - method close is threadsafe
  - added method getState
JCLOUDS-100. Add AWSServerErrorRetryHandler, with an increased back
off time.
Do not repeat array type in initializers