Jenkins job switch to multibranch pipeline

[Juan Pablo Santos Rodríguez <ju...@gmail.com>]

Hi,

as people subscribed to commits@j.a.o must surely noticed (apologies on the
ton of e-mails!), the CI job has been moved to a multibranch pipeline. This
has several advantages

* each pr / branch is built in its own workspace on the jenkins job, so
it's easy to see which branch is being built
* builds on the master branch are the only one that
** send e-mails with build results, in order to keep noise to a minimum
** publish javadocs & updates the static website, so feedback in other
branches is faster (about 1/3 of the time when compared to master branch)
* PRs on github get additional checks, so if a PR breaks the build, we'll
notice before merging
* we got separate SonarQube analysis for each branch built

The URL of the job is the same as before, the previous job has been renamed
to ci-old, is disabled and will be deleted once we're sure that the new one
performs as expected.

There's still some room for improvement, so I suppose I'll be making minor
edits on the job next week(s), but as usual, comments, edits, patches, etc.
are more than welcome.


cheers,
juan pablo