initial commit
improv: added git dependency
improv: separate data volume

`/var/lib/jenkins` is exposed as a volume. Plugins are installed
only once and after the data store mapping is established.
Safely update and install packages

Having the apt-get update and then install in separate RUN statements potentially means the install will fail, despite the presence of the update. One-lining the build here should fix that.
Merge pull request #1 from grahamc/patch-1

Safely update and install packages
Switched remote