headless change flag to (always[true], ifneeded[false], never)

[valentinedwv]

as I moved the ability to run headless into acquire to handle multiple threading, I hit that if there is no headless, run will fail.
Have ability to disable headless, and run if headless is not available.

We should just change the headless flag on a source to three options,

• always - or formerly, true
• ifneeded - or formerly, false
• never - do not run headless, do not configure, (formerly headlesswait = -1)

Also, if headless is not available and if needed or never, do not stop run