Add servoadapter to interface with cros-servod

We intend to delete this after cros-servod has implemented its
functionality without depending on labstation-specific custom binaries.

For now, this library implements cros-servod related functionality on
the client side over ExecCmd() interface.

BUG=None
TEST=local testing

Change-Id: I725da9917fdb81ace810fef35f24e53c28b75b28
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3645939
Reviewed-by: Jaques Clapauch <jaquesc@google.com>
Commit-Queue: Jaques Clapauch <jaquesc@google.com>
Auto-Submit: Sergey Frolov <sfrolov@google.com>
Tested-by: Sergey Frolov <sfrolov@google.com>
3 files changed