leap_cli should exit with exitcodes>0 when it fails

leap -v 2 deploy tor1  
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/dns.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/monitor.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/webapp.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/openvpn.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/couchdb.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/ca.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/services/tor.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/tags/local.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/tags/production.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/common.json
 = loading /home/varac/dev/Projects/Leap/dev/walkthrough/leap_platform/provider_base/provider.json
 = loading nodes/monitor.json
 = loading nodes/webapp.json
 = loading nodes/openvpn.json
 = loading nodes/couchdb.json
 = loading nodes/ca.json
 = loading nodes/tor.json
 = loading common.json
 = loading provider.json
 = loading secrets.json
 = ran git submodule status 2>&1
 = Could not match any nodes from '["tor1"]'
 = bailing out 

--- walkthrough/rewire ‹master› » echo $?
0

this is crucial for our automatic testing setup.

In particular, it is very important exit with a non-zero exitcode on any puppet error.

(from redmine: created on 2013-02-09, closed on 2013-03-14, relates #1627 (closed))