Small fixes to udev rules and initramfs hook

These two patches sorted out the issues I had when installing bcache-tools on Ubuntu 14.04.

The test for floppy drives removed several pauses when booting the system. These would show up in dmesg as ~8 second pauses:

[    4.022378] random: nonblocking pool is initialized
[   13.284572] end_request: I/O error, dev fd0, sector 0
[   25.444523] end_request: I/O error, dev fd0, sector 0
[   25.444526] Buffer I/O error on device fd0, logical block 0
[   32.749886] EXT4-fs (sda1): mounted filesystem with ordered data
mode. Opts: (null)

The hook file modification allows any customised udev rule in /etc/udev/rules.d/ to be copied into the initramfs image.