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
refactor keystone.conf template specs

add tests for every tunable.  organize code layout to reflect actual
template layout (group tests, in order).  also 3x performance gain by
collapsing 50+ chef converges into one.  remove 'pending' tests in
other platforms since there are no platform-specific tunables.

Change-Id: Ib0dc3728a5b0c81bf3b3a36a1a644a7a2fff5910
Closes-Bug: #1182562