Bug 20079: Display stack trace for development installations

Bug 20079: Display stack trace for development installations

"""The default value is development, which causes plackup to
load the middleware components: AccessLog, StackTrace, and Lint unless
--no-default-middleware is set."""

Test plan:
Confirm that the stack trace is displayed when something is wrong (die somewhere to test)
for dev installations (inside a devbox)
The -E flag must remain deployment for non-dev installs

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>