tidy up confirmedit role

Replace pip-install of PIL with "python-imaging" library, since Trusty's is
sufficiently up-to-date. Update the name of DejaVu Sans. Declare Captcha dir
using Puppet. Use variables to break up captcha generation exec. Make captcha
generation refreshonly.

Change-Id: I3ad17d9a14a3f2f043833d6c61b2d10dbd9a5369
Update MediaWiki-Vagrant for Trusty

[Detailed commit message goes here.]

Change-Id: I999bd8d4f537cc364e2484e95491ee9e9afbf8e8