[c-nsp] Correct syntax for Boot system

[Scott Voll]

I have always used

boot system flash:xxxxxx.bin or boot system bootflash:xxxx.bin

did the syntax change to boot system flash flash0:xxxxx.bin???

I have a new 4331 that without the extra flash it failed to boot.   Is this
new?  did I miss the memo?

does this carry over to ASRs and the older 29xx/39xx platforms?

I'm booting a bunch of remote routers and don't want to be driving to
recover them from a simple mistake I missed.

TIA

Scott