Support Xvfb in launcher

[Krinkle]

Having the ability to let Karma create dedicated Xvfb displays for launched browsers would be quite valuable.

See also:

• Add ability to use xvfb-run for google-chrome karma-chrome-launcher#20
• https://github.com/proxv/node-xvfb
• https://groups.google.com/d/msg/karma-users/JGVChr3d4JI/iysKBpcFSUQJ
• https://groups.google.com/d/msg/karma-users/Q4XWo7VoT2A/tb-me5bDHcwJ

[scamden]

+1

[heldr]

+1

[forkingpath]

+1

[r4j4h]

+1

[dtheodor]

👍

[adamthesax]

👍

[dvv]

+1
TIA

[cwegener]

👍

[PavelKonon]

👍