Upgrading the docker image from the unsupported Ubuntu 15.10 release
to the 16.04 LTS release let us build the win32 binary successfully.
DON'T BUILD
MozReview-Commit-ID: 9Z0MPsMqyTu
--HG--
rename : testing/geckodriver/i686-trusty/Dockerfile => testing/geckodriver/i686-xenial/Dockerfile
extra : rebase_source : 5595355b978e17c201b6de5ed0acbb35ffee6344
Henrik Skupin