Send image build/deploy transcripts to syslog

The output of k8s image build and deployments are now logged to the scap.k8s.build and scap.k8s.deploy channels respectively as single messages after the operation completes. Scap's logging setup has been configured to ensure that these messages do not show up on the console under normal conditions.

Other changes:

Got rid of K8sOps._ensure_file_deleted and changed utils.subprocess_check_run_quietly_if_ok to always open and truncate the output file instead of appending. This simplifies the function too.

Bug: T323939