Suggestions for properly mounting 4' shop light
Replace that goofy Edison socket with a coverplate for a receptacle.  Now you have a dual receptacle that is switched by the garage light switch. 



Hang the lamps by chains.  And then plug their plugs into the receptacle.  

It gives you the versatility to move the lights around to suit, and allows easy swap or addition of a fixture.

Flexible cordage, as a replacement for fixed wiring, is only allowed in certain cases -- luminaires are one of them.  It is legal to use plug and socket when the plug is accessible (e.g. not behind a drop ceiling, unless your AHJ authorizes that).