bin/solr -e cloud
Please enter the port for node1 
Oops! Looks like port 8983 is already being used by another process. Please choose a different port.
Looking at the script, it uses:
which gave the output:
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
Google 365 upayavira 130u IPv6 0xab1d227df2e5a7db 0t0 TCP [::1]:49889->[::1]:8983 (ESTABLISHED)
java 10889 upayavira 118u IPv6 0xab1d227df2e73ddb 0t0 TCP *:8983 (LISTEN)
java 10889 upayavira 134u IPv6 0xab1d227df2e756db 0t0 TCP [::1]:8983->[::1]:49889 (ESTABLISHED)
This was connections Google Chrome was attempting to make to Solr.
Replacing the above line with this:
PORT_IN_USE=`lsof -Pni:$CLOUD_PORT | grep LISTEN`
resolved the issue. Very simple patch attached.