fixes bug 1043681

invert the -z test to -n when trying to figure out if we're building in a ci environment or not.
Merge pull request #2258 from lonnen/1043681-fo-realz

fixes bug 1043681
Revert "Merge pull request #2255 from mozilla/revert-2249-fix-bug-1038340-make-to-bash"

This reverts commit faea35b52cdd8c2c3a6e14213e0c77cecccf3522, reversing
changes made to ed8095aaa198caec3ddf5b902649b4be759699c4.
Coverage slipped in during transition to scripts
Remove extra make install line from build.sh
Don't set PREFIX unless unset in install.sh
Remove extra dollar signs from install script vars
Replace VIRTUALENV with {VIRTUAL_ENV} variable.
Remove xunit from nosetest runs.
Activate the virtualenv if hasn't already been
Export the VIRTUAL_ENV after activating it.
Set a default for VIRTUAL_ENV
Replace cd commands with pushd/popd in scripts
Source bootstrap, test, and install in build.sh
Move bash arguments to top of scripts.
Replace hardcoded virtualenv in webapp-django
Replace hardcoded virtualenv in rabbitmq tests