Use sha of validated commit to publish snapshot

Later jobs also know this sha (it's propagated by jenkins),
so that they can easily resolve it. Currently used by IDE validation.

Before, we were using the sha of current HEAD, which is the merge
commit of merging the tested commit into the target branch.
This is not information readily available in downstream jobs, however.
Merge pull request #1 from adriaanm/publish-commit-sha

Publish commit sha
remove publishMaven -- no longer used for ide validation
First version of scala-pr job

first step towards more modular and parallellizable PR validation

goal:
  1. build a minimal distribution -- just the jars (building quick using STARR)
  2. in parallel
    - build docs
    - run partest test suite
    - run junit tests
    - run stability test
    - run rangepos tests
    - run IDE integration
    - run other dbuild integrations