Always return a result from database command methods

[brkn]

Description

• Return SystemCall::Result objects from guard checks at database util class methods instead of primitive true values. This removes the need for checking the object of the returned.

• Replace Failure Struct with a class to remove warnings at test outputs. Failure constant redefined

[alassek]

I’m in favor of the motivation here, to reduce type-checking results by making them work consistently. But I’m not sure I like the specific solution of faking shell command output. I don’t think we should be capturing exit codes for executions that didn’t happen.

[brkn]

Thank you for the comment.

I’m not sure I like the specific solution of faking shell command output.

To understand it better, which one you don't like:

A) These database methods (like exec_drop_command) returning SystemCall::Result instances when we didn't do system calls on early exits

B) These database methods (like exec_drop_command) returning an object that respond to #exit_code calls when we didn't do system calls on early exits