Refactor remote image remote instance create function.

- Phase out create AVD via instance metadata.
- Remote image remote instance & local image remote instance use the same
  factory class.
- Refactor remote instances operations with ssh command.

Bug:134919522
Test: acloud-dev create
Change-Id: I082e48a172c245ba4d726a145b0a2657862aa49d
5 files changed