add error handling

lib/docker_manager/upgrader.rb

@@ -30,6 +30,9 @@ class DockerManager::Upgrader
     else
       log("Did not find unicorn launcher")
     end
+  rescue
+    STDERR.puts("Docker Manager: FAILED TO UPGRADE")
+    raise
   end
 
   def run(cmd)
@@ -37,6 +40,11 @@ class DockerManager::Upgrader
     IO.popen("cd #{Rails.root} && #{cmd} 2>&1") do |line|
       log(line.read)
     end
+
+    unless $?.success?
+      STDERR.puts("FAILED: #{cmd}")
+      raise RuntimeError
+    end
   end
 
   def log(message)