Support creating SAS for Azure stoage services

1. Support new commands
   * azure storage container sas create
   * azure storage blob sas create
   * azure storage table sas create
   * azure storage queue sas create
2. Fix bugs: some of storage unit tests cannot be run live
  
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Why add the extra level of describe? You only have the single scenario (the `it` method) and no extra setup or teardown requirements?