This group is for rock musicians ready to perform out in clubs without the long-term commitment - and hassle - of joining a band. Phil Brandt, organizer of the successful "Pick, Play and Perform Guitar Group" - which regularly played out in the Village - is creating "4 ON THE FLOOR." Here's how it works: Four musicians from the group will be paired together to create a "band." Each band will give themselves a name and have two rehearsals to select and rehearse four rock cover songs. At the show …