Relax spawn tight tolerance

[chapulina]

I was too ambitious on #61, the current tight tolerance is flaky, see failure

2021-11-05T03:25:43.8355456Z 9: /home/developer/lrauv_ws/src/lrauv/lrauv_ignition_plugins/test/test_spawn.cc:161: Failure
2021-11-05T03:25:43.8356431Z 9: The difference between 0.0 and poses1.back().Pos().X() is 2.1789064913657771e-06, which exceeds tightTol, where
2021-11-05T03:25:43.8356995Z 9: 0.0 evaluates to 0,
2021-11-05T03:25:43.8357586Z 9: poses1.back().Pos().X() evaluates to -2.1789064913657771e-06, and
2021-11-05T03:25:43.8358198Z 9: tightTol evaluates to 9.9999999999999995e-07.

[tfoote]

Yeah, that's pretty tight.