LIB-45: test different default candidates for existance

For Linux/BSD/Solaris we can probably fix a couple of default drive problems with checking for the existance of multiple candidates.

Debian/Ubuntu only seems to create /dev/cdrom1, rather than /dev/cdrom. We just try both. And return the one that works or the first one.

Parsing /proc/sys/dev/cdrom/info is probably not necessary.

@phw: You might be interested in this. since you reported only having /dev/cdrom1 (which I could reproduce on a new Debian installation).

This is tracked in:
http://tickets.musicbrainz.org/browse/LIB-45