Flux release 1.4.1

This release fixes some wrinkles in the new YAML updating code, so
that YAML multidocs and kubernetes List resources are fully
supported.

It also introduces the fluxctl sync command, which tells Flux to
update from git and apply to Kubernetes -- as requested in
TGI Kubernetes!

Fixes

• Write whole files back after updates, so that multidocs and Lists
  aren't overwritten. A symptom of the problem was that a release
  would return an error something like "Verification failed: resources
  {...} were present before update and not after"
  weaveworks/flux#1137
• Interpret and update CronJob manifests correctly
  weaveworks/flux#1133

Improvements

• Return a more helpful message when Flux can't parse YAML files
  weaveworks/flux#1141
• Bake SSH config into the global location (/etc/ssh), so that it's
  easier to override it by mounting a ConfigMap into /root/.ssh/
  weaveworks/flux#1154
• Reduce the size of list-images API/RPC responses by sending only the
  image metadata that's requested
  weaveworks/flux#913