Fix docker build issues.
Fix docker build issues.

* `apt-get update` gets cached and in case it fails the whole build
  fails
* It's best practice to run all `apt` related commands to a single RUN

akatsoulas/mozillians,fxa90id/mozillians,fxa90id/mozillians,mozilla/mozillians,johngian/mozillians,akatsoulas/mozillians,akatsoulas/mozillians,mozilla/mozillians,akatsoulas/mozillians,fxa90id/mozillians,johngian/mozillians,mozilla/mozillians,fxa90id/mozillians,johngian/mozillians,johngian/mozillians,mozilla/mozillians