[sonic-installer] Hyphens instead of underscores in command and subcommands

[jleveque]

Replace underscores with hyphens in all sonic-installer subcommands as well as the root command itself.

• Install two entry points for sonic-installer: sonic-installer and sonic_installer. This allows for backward compatibility and time for users to transition from using the underscore versions to the hyphenated versions.

• Replace underscores with hyphens in the following subcommands:

  set-default
  set-next-boot
  binary-version
  upgrade-docker
  rollback-docker
  

  • Also add aliases from the underscore versions of these subcommnds to the new hyphenated subcommands to allow for backward compatibility and time for users to transition from using the underscore versions to the hyphenated versions.

• Print deprecation warnings to stderr if issued command line contains any deprecated versions with underscores

• Bonus: Addition of the AliasedGroup base class also adds support for abbreviated subcommands

• Fixed some style issues which did not align with PEP8 standards

• Eliminate duplicate code by adding DOCKER_CONTAINER_LIST; Remove unknown 'amon' container from the list

This is work towards resolving issue #982. We can set a deprecation date for the underscore versions of the commands, and when that date arrives, we can simply delete all aliases and deprecation warnings.

[jleveque]

Retest this please