Add command to kill stray mojo shell servers so we don't have to remember it

R=ppi@chromium.org, ppi

Review URL: https://codereview.chromium.org/1291733002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: 9f724011b8a4ea7d3db07e50c2de64d5f3ecf7f2

devtoolslib/http_server.py

diff --git a/devtoolslib/http_server.py b/devtoolslib/http_server.py
index 16c76a9..d8a2757 100644
--- a/devtoolslib/http_server.py
+++ b/devtoolslib/http_server.py
@@ -222,7 +222,8 @@
     print 'Failed to start http server for %s on port %d: %s.' % (
         str(mappings), host_port, os.strerror(error_code))
     if error_code == errno.EADDRINUSE:
-      print ('  Run `fuser %d/tcp` to find out which process is using the port.'
+      print ('  Run `fuser %d/tcp` to find out which process is using the port;'
              % host_port)
+      print ('  or `fuser -k %d/tcp` terminate it.' % host_port)
     print '---'
     raise