Commits 0eed77127592323d89f56c215a15374a1aaae110 and
614a1e3fa2d731d4719f03912b1b87fb4fd309cb caused a ~150M increase of the image
size. Increase the image size limit by 200M until the situation is addressed.
* gnu/tests/install.scm (%simple-installation-script,
%extlinux-gpt-installation-script, %simple-installation-script-for-/dev/vda,
%raid-root-installation-script, %encrypted-root-installation-script): Increase
image size limit by 200M.