add 'flume sink' and 'flume source' commands to ease debugging.

Currently users can use the 'flume dump <source>' command to setup a one shot instance that dumps to console. This actually issues a expands to this cumbersome command :

Doing its inverse is common when debugging. Since this is a pair, it makes sense to give them related names. Suggested names include:

flume source <source> ==> flume node_nowatch -n dump -s -1 -c 'dump:$1|console;'

flume sink <sink> ==> flume node_nowatch -n dump -s -1 -c 'dump:console|$1;'