This change adds a new deploy-interface custom-agent that is essentially
the direct deploy without the write_image step and without bootloader
handling. It's targeted at deployments that need to write the image
differently, while keeping all other aspects the same.
The existing AgentDeploy becomes a subclass of the new CustomAgentDeploy
class, serving as a convenient base class for downstream deploy
interfaces that use IPA.
Change-Id: Ie126ce677c79f102e382305650bddb7f09834483
Story: #2008719
Task: #42059
e85a36fe36