Bug#1095028: xvfb: Race condition in xvfb-run

[Santiago Vila <sanvila@debian.org>]

severity 1093686 grave
affects 1093686 src:rhythmbox src:merkaartor src:libktorrent src:maliit-keyboard src:kf6-kconfig
thanks

Hello Simon. I was going to comment on #1093686 against src:rhythmbox, but then I realized
this is very likely a manifestation of this bug in xvfb-run, which is probably
the reason why several other packages FTBFS randomly as well.

In fact, all the packages below use xvfb-run in their tests, and I get random failures
with the following failure rates:

0.260 rhythmbox  (26/100)
  reported as #1093686
0.270 merkaartor  (27/100)
  (not reported yet)
0.340 libktorrent  (34/100)
  (not reported yet)
0.400 maliit-keyboard  (40/100)
  (not reported yet)
0.411 kf6-kconfig  (37/90)
  (not reported yet)

Build logs available here:

https://people.debian.org/~sanvila/build-logs/xvfb/

According to the general guidelines given by Paul in Bug #1057562,
I think all the above issues should be considered as RC.

(Note: In the above, I'm using a threshold of 1/4, which is a little
bit more permissive than the 1/6 figure suggested by Paul).

Thanks.