Arvados

1. Turn off loading spinner and display error message when "load tab" ajax request fails
2. Improve error message ("log not available"?)
3. Do not even offer a Log tab if log collection lookup fails
4. Test cases for "collection.find fails" and "collection.find succeeds but arv-get fails"

#<RuntimeError: Path not found [API: 404]>
/home/tomclegg/arvados/apps/workbench/app/models/arvados_api_client.rb:107:in `api'
...
/home/tomclegg/arvados/apps/workbench/app/models/arvados_base.rb:108:in `find' 
/home/tomclegg/arvados/apps/workbench/app/views/jobs/_show_log.html.erb:24:in `_app_views_jobs__show_log_html_erb___2688258275434600425_57780620'