TEST: Allow OVMF non-volatile variables to be saved across QEMU runs

Modified the EFI test script to make a local copy of the OVMF binary
and load it in QEMU using the -pflash option rather than -bios. This
means that OVMF will save it's non-volatile variables in the local copy
of the OVMF binary and persist across QEMU runs. Also changed the
default settings to not output the primary console to the serial port -
KBoot treats the on-screen and serial consoles differently.