[bazel] Fix use of entrypoint with run_commands_root
[bazel] Fix use of entrypoint with run_commands_root

"--entrypoint /bin/echo" was not executing the commands specified to container_run_and_commit, it was doing a no-op. Removing it.

Handling the entrypoint problem by creating a container_image with no entrypoint to use in container_run_and_commit.
The next container_image rule will put back the entrypoint.

Bug: skia:12506
Bug: skia:12509
Change-Id: I30d1da47dc5b1d626b70cb172722959782f76ca1
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/457576
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Reviewed-by: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot