## Proposed Changes
Adds some improvements I found when playing around with local testnets in #3335:
- When trying to kill processes, do not exit on a failure. (If a node fails to start due to a bug, the PID associated with it no longer exists. When trying to tear down the testnets, an error will be raised when it tries that PID and then will not try any PIDs following it. This change means it will continue and tear down the rest of the network.
- When starting the testnet, set `ulimit` to a high number. This allows the VCs to import 1000s of validators without running into limitations.
## Issue Addressed
Resolves https://github.com/sigp/lighthouse/issues/2763
## Proposed Changes
- Add a workflow which tests that local testnet starts successfully
- Added `set` option into the scripts in order to fail fast so that we can notice errors during starting local testnet.
- Fix errors on MacOS
- The redirect `&>>` is supported since bash v4 but the version bundled in macOS(11.6.1) is v3. a54f119c9b
