Preserve backtraces when re-raising errors

[Sharpie]

This commit updates locations where StandardError instances are rescued and re-raised as VSphereError to preserve the backtrace info of the original errors along with the message. This change makes debugging easier as the backtrace leads to the location where the error originated instead of the rescue block where it was re-raised.

[Sharpie]

Test failures appear to be unrelated, likely fixed by PR #283.