better defaults for tests with NUM_DOMAINS > 1

[lsf37]

We are currently not running any tests with NUM_DOMAINS > 1 and the defaults in sel4test lead to extremely slow test execution.

This PR picks nicer defaults:

• only 4 domains instead of 16
• give domain 0 a long time slice
• some schedule variety in the first 4 domains
• shortest period of 2 ticks

This should enable faster tests even under simulation.

This PR is a prerequisite for seL4/ci-actions#248.

[lsf37]

@robs-cse this should be close to the values you used in your test run. Does this look overall reasonable?