Bug#747361: sdformat: FTBFS: most odd-numbered tests time out

[Aaron M. Ucko]

Source: sdformat
Version: 2.0.0-1
Severity: serious
Justification: fails to build from source

Automated builds of sdformat have all been encountering test timeouts,
in a distinctive pattern:

  The following tests FAILED:
  	  1 - INTEGRATION_audio (Timeout)
  	  3 - INTEGRATION_cfm_damping_implicit_spring_damper (Timeout)
  	  5 - INTEGRATION_fixed_joint_reduction (Timeout)
  	  7 - INTEGRATION_joint_axis_frame (Timeout)
  	  9 - INTEGRATION_provide_feedback (Timeout)
  	  11 - PERFORMANCE_parser_urdf (Timeout)
  	  13 - UNIT_SDF_TEST (Timeout)
  	  15 - UNIT_Console_TEST (Timeout)
  	  19 - UNIT_parser_urdf_TEST (Timeout)

It's not clear why, but I do see that the tests were always running in
parallel; could they somehow interfere with each other?  At any rate,
please do take a look.

Thanks!