app autoscaler cli plugin v1.1.0

Adding support for:

• Align with App-autoscaler v1.1.0 release
  • https://github.com/cloudfoundry-incubator/app-autoscaler-release/releases/tag/v1.1.0
  • https://bosh.io/releases/github.com/cloudfoundry-incubator/app-autoscaler-release?all=1
• Set default autoscaler api by name convention "autoscaler.". So, in most of the case, the end-user won't need to run "cf asa" separately. But if "autoscaler." is not accessible, the default "autoscaler api endpoint" will be left as empty, so that the end-user need to assign it manually.
• Change the autoscaler endpoint automatically according to name convention "autoscaler." when cf target changes.
• Remove instances metric support on "cf asm" command
• With command "cf asm" and "cf ash", by default, only the most recent results will be returned (default record number is 50).
• With command "cf asm" and "cf ash", you can define the number you want to return by option "--number"
• Fix unmarshal failure when handling error response.