Intermittent test failure in circuitpadding/circuitpadding_wronghop

Try running circuitpadding_wronghop in a loop, like this:

while ./src/test/test circuitpadding/circuitpadding_wronghop ; do true; done

After a minute or two it will fail with an error like this:

  FAIL src/test/test_circuitpadding.c:1346: assert(n_client_cells OP_EQ 2): 3 vs 2

or sometimes like this

circuitpadding/circuitpadding_wronghop: [forking] 
  FAIL src/test/test_circuitpadding.c:1336: assert(n_client_cells OP_EQ 1): 2 vs 1