Interference of bilby command line args

If users write a script/module which uses the command line arguments as input, there can be interference between their definition of the command line arguments and those interpretted by bilby.

On the one hand, this is useful as arguments such as --clean or --use-cached pass through and things behave as expected. On the other hand, the -t shorthand for --test [1] can cause a lot of confusion when suddenly the scripts run in "test" mode (i.e. only run for 100 steps then stop.

The simple fix is to remove the -t shorthand, replace --test with something more verbose such as --bilby-test-mode that no user is likely to accidentally use and correspondingly update all the tests which use this.

[1] For those interested, the --test mode is used when testing the samplers just to check that they will sample for a few hundred steps and then stop.