v4l2: STREAMOFF command wait worker thread exit/cleanup with condition broadcast

worker thread may become conditionaly wait after
one-time broadcast from STREAMOFF command
tests: add vp8/jpeg support for v4l2decode

jpeg may have one frame only, take special care of it
jpeg may output as IMC1/IMC3, we fix the output format to NV12
to simplify frame dump
tests: use decodehelp.h in v4l2decode
tests: add possibleWait(), it helps one frame jpeg display