Meaningful error on immediate omxplayer death

[willprice]

Feature Request: Exception on omxplayer spawn failure

Description

When omxplayer fails to spawn due to invalid command args or similar, a DBusConnectionError is raised which is very unhelpful, it doesn't indicate what the issue is, we should catch this and output a new error.

Example use case

# Raises error due to malformed `args` parameter (should be shell split)
OMXPlayer("blah.mp4", args=["-o hdmi --no-osd"])

[matthijskooijman]

To actually capture a meaningful error message in this case, it might be needed to not redirect stdout as well, see #205.