Fixes for SH, typo, prompt consistency

Added the data centre names to the prompt & fixed a typo,

For some reason I instinctively use "sh scriptname" with this sort of thing, so:

I've got rid of the bash specific alias of == to = inside of [] and stopped sh skipping straight over the sanity check (I didn't  notice there was supposed to be one before reading the source) by giving a variable name to the read -p line