[Keyman] Minor changes
[Keyman] Minor changes

- don't create jobs for PRs for non-pipeline jobs
- all packages should build on Xenial
- Pipeline job no longer experimental

Change-Id: Ice552d87d3c661abcc2dd42adab83796a5bbbf33

sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts