Compile YCP logical operators as Ruby logical operators

Previously the logical operators were compiled as |Ops| calls, which
didn't respect short-circuiting.

Compiling as Ruby logical operators can introduce wrong behavior in some
edge cases, but that is unlikely. The only possible implementation that
would respect both exact semantics in all edge cases and sort-circuiting
would need to use lambdas, which would make the resulting code
unreadable.

Based on a pull request by Josef Reidinger:

  https://github.com/yast/y2r/pull/6