add blacklist for sd numbers

[alcir]

If you know there are sd that may have errors (i.e. LCDRIVE, Product Virtual CD, cdrom readers), and you do not care, you can blacklist such sd

[bahamas10]

I like the idea of this, but the implementation should be reworked. Right now, sd1 is the name of a proper device on our servers

$ /opt/local/libexec/nagios/check_disk_busy 
ok: disk 72% busy (warning=90%, critical=95%, disk=sd1)|disk_busy=72

Perhaps the blacklist should be able to be passed in as a command line arg... ie.

check_disk_busy -b sd1,sd2,sd3