Allow the use of different displays for functional test

Using the DISPLAY variable allows a less "obnoxious" running of
tests in an Xserver, preventing popup windows and accidental
interaction with a running test environment.
add wait until logic around dynamic field
Merge pull request #48 from zanata/run-xnest

Allow the use of different displays for functional test
Merge pull request #50 from zanata/fix-functional-test

add wait until logic around dynamic field