Guard against if ipv4Gateway is nil, removed fore unwrap

[manojmahapatra]

Summary

• Guarded against ipv4Gateway if nil and throw ContainerizationError(.invalidState, ...) instead of force unwraping
• Added a unit test ContainerManagerTests.testCreateThrowsWhenGatewayMissing

Testing

• make test passed.

[jglogan]

@manojmahapatra Please commit a make fmt change.

You can install a pre-commit hook to check this at commit time: make pre-commit.

[manojmahapatra]

@manojmahapatra Please commit a make fmt change.

You can install a pre-commit hook to check this at commit time: make pre-commit.

yes, thank you. It was in my todo, but I forgot somehow. :(

[jglogan]

Looks good @manojmahapatra, thank you!

[jglogan]

@manojmahapatra You'll need to repush with signed commits; see: https://github.com/apple/containerization/blob/main/CONTRIBUTING.md#pull-requests

[manojmahapatra]

Ugh.. dont know what's going on my end. Done, thanks @jglogan

[jglogan]

@manojmahapatra merged, thank you!