CI: Create generic jenkinsfile

This is a generic jenkinsfile to build Asterisk and optionally
perform one or more of the following:
 * Publish the API docs to the wiki
 * Run the Unit tests
 * Run Testsuite Tests

This job can be triggered manually from Jenkins or be triggered
automatically on a schedule based on a cron string.

Change-Id: Id9d22a778a1916b666e0e700af2b9f1bacda0852