Triggering PR build requests

[Leif Hedstrom <zw...@apache.org>]

Hi all,

since we’re depending more and more on Github PR builds with our Jenkins, I’ve made some additional changes to allow for selective triggering individual checks to build. So, all committers can now do the following in a comment on a PR:

	[approve ci]  - Triggers all builds
	[approve ci autest] - Only builds the autest check
	[approve ci RAT] - Only builds the RAT check
	[approve ci clang-analyzer] - Only builds the clang-analyzer check
	[approve ci clang-format] - Only builds the clang-format check
	[approve ci linux] - Only builds the Linux check
	[approve ci freebsd] - Only builds the FreeBSD check
	[approve ci icc] - only builds the Intel compiler check


Note: All committers are automatically having their new PRs trigger builds. I.e. there’s no reason to manually trigger the build after you (the committer) “git push” a PR (or an update to a PR). For-non committer PRs, a committer must [approve ci] still to trigger the build, and make sure you only do that after you have examined the PR for any potential damaging commands.

Cheers,

— leif