qemuxml2argvmock: Pretend FW blobs are always present

qemuxml2argvmock: Pretend FW blobs are always present

Soon, the QEMU driver, specifically the part that picks firmware
based on firmware descriptor files (qemu_firmware.c) is going to
check for the presence of those firmware blobs (well, for their
realpath()). Just collect the list of all blobs we use in our
tests and mock virFileCanonicalizePath() so that for any path on
that list its strdup()-ed version is returned.

This means, qemuxmlconftest won't touch host files really.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>