When I added the Dockerfile I initially wrote it in a 2 step fetch & build, to try to avoid recompiling the whole thing every time some patch from one of the devs was pushed to our building branch. This, whoever, creates problems sometimes due to how the build system for pjproject is generated when building asterisk, so let's drop the 2stage setup to avoid problems fetching from different branches, etc.
asterisk-master: Build from jolly/work branch by default
That one will not be the final branch, but it's the one where most of the development is happening. Hence, switch to that branch by default for now, so that jenkins nightly job runs that branch.
