Honour WIP labels and notes - do not build under Jenkins

[grahamwhaley]

Currently I believe our Jenkins is not configured to spot 'WIP' or 'do-not-merge' labels, and will build them anyhow (with likely failures and wasted CI resource time)
I think we should add probably 'WIP' to the github pull requester build advanced boxes of:
Skip build phrase
and
List of GitHub labels for which the build should not be triggered.

We probably want to define exactly what 'WIP' and 'do-not-merge' mean. I propose we do that in the CONTRIB or similar docs of the runtime repo. Something like:

what	meaning
WIP label	Work In Progress - do not merge, and do not build under the CIs
WIP in subject or body	similarly - but - WIP label is preferred or as-well, as easier to see in githug
do-not-merge label	CIs will attempt to build, but PR should not be merged - useful for testing something will build and pass tests without having it merged immediately into the codebase

@sboeuf @chavafg @jodh-intel - thoughts?