extra/runner/run: Don't run more tests if v4l2 capture device not found
extra/runner/run: Don't run more tests if v4l2 capture device not found

This happens, for example, when the cleaners bump the power button on my
Hauppauge HDPVR that's running tests overnight.

Checking for "/dev/v" will match "/dev/video0" as well as
"/dev/v4l/by-id/..." (I use the latter in my source pipeline if the PC
has multiple devices connected, because the "by-id" path doesn't change
across PC reboots).

martynjarvis/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester