Deal with versions of genisoimage that don't support -efi-boot.
Deal with versions of genisoimage that don't support -efi-boot.

Non-Fedora, unpatched versions of genisoimage don't support
the -efi-boot flag.  Skip the mac uefi test on those
platforms.

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@gmail.com>

clalancette/pyiso,clalancette/pycdlib