qemu.tests.floppy: make mount tool auto-detect filesystem in floppy

Not all floppy was be format to vfat filesystem, so remove it to make it
auto-detect by 'mount' tool.

Signed-off-by: Xu Tian <xutian@redhat.com>
Merge pull request #117 from xutian/floppy_test

qemu.tests.floppy: make mount tool auto-detect filesystem in floppy