install.sh: Make OF1.3 Netbee location cmd-line configurable
install.sh: Make OF1.3 Netbee location cmd-line configurable

If NBEEURL is defined when running install.sh, use that location.

Enables use of a local mirror for netbee download.

Thanks to David Erickson for the code.

mininet/mininet,mininet/mininet,mininet/mininet