Simplify running tests even further

Now you can just say:

  $ nix-build '<nixos/tests/login.nix>'

You can still get the driver script for interactive testing:

  $ nix-build '<nixos/tests/login.nix>' -A driver
  $ ./result/bin/nixos-test-driver
Add script to create and upload GCE image.
kde-4.10: Remove
Add a recipe for installing "watch" from procps (#2227)
Fix installer test evaluation
Rewrite ‘with pkgs.lib’ -> ‘with lib’

Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
gnome3: add gtk3 to system packages for gtk-update-icon-cache

Updating the icon-cache lets gnome-shell show app icons in the activity
Update section on writing tests
Manual: Add some IDs
Update mtr to 0.85, and allow building on any unix
Add missing file
linux: Don't use underscores in the timestamp
nixos opengl: add s2tc to mesa drivers by default

Close #2200. Thanks to @cpages for suggesting and testing this.
mesa: have all output on /run/opengl-driver{,-32}

Fixes #2242 in a different way (cleaner, I hope).
gsasl: fix build on Darwin (close #2260, fixes #2259)

@vcunat rewrote with "more standard" optional functions.
Allow lua5 to build as a dylib on Darwin
On Darwin, set NO_APPLE_COMMON_CRYPTO=1 for git builds
gnome-shell: maybe fix the background corruption bug
gnome3: add gnome-menus and shared_mime_info packages to find applications
linux: Update to 3.13.10