Fix 'Avoid rescuing the Exception class.' warnings

Rubocop warns about doing a rescue on Exception:
"Avoid rescuing the Exception class. This will trap signals
and calls to exit, requiring you to kill -9the process."

According to the style guide, we should be catching StandardError
instead, which doesn't trap exit signals. This patch addresses that
issue.

Change-Id: I6cf3e6b5cecfdc4d412789d75e1af9e6d53c6e8d