Pylabs: Return exit code of 'start' and 'catchupOnly' invocations

See: ARAKOON-383
See: http://jira.incubaid.com/browse/ARAKOON-383
See: ARAKOON-379
See: http://jira.incubaid.com/browse/ARAKOON-379
Pylabs: Test 'wrapper' exit code propagation

See: 872ddbad2ed4f35bb248d9c88c6dca6da49a9e59
See: ARAKOON-383
See: http://jira.incubaid.com/browse/ARAKOON-383
See: ARAKOON-379
See: http://jira.incubaid.com/browse/ARAKOON-379