post-processor/vagrant: test for user variables in vagrantfile_template [GH-1125]

Previously fixed in a47610879fcd5e2871b3e088e40d368a2915455f

Closes #1125
post-processor/vagrant: process templates in Configure
Merge pull request #1694 from ceh/issue-1125

Test for user variables in vagrantfile_template [GH-1125]