ssh_host.py: measurement of host.ssh times

Add the measurement of the host.run to have better understanding
about what is happending to the network ssh calls.

BUG=chromium:729161
TEST=ran test_that graphics_Sanity

Result by logging inside metrics.SecondsTimer experimentally
06/05 15:33:38.153 DEBUG| ssh_host:0286| Running (ssh) '/bin/uname -r'
06/05 15:33:38.199 DEBUG|    utils:0298| [stdout] 4.4.44-07362-g31d7be5
06/05 15:33:38.200 DEBUG|  metrics:0253| ../master_ssh_time dt: 0.05

Change-Id: I09d5405f3c6823bd3122eadc78084a0f4f0dfd2a
Reviewed-on: https://chromium-review.googlesource.com/525016
Commit-Ready: Po-Hsien Wang <pwang@chromium.org>
Tested-by: Po-Hsien Wang <pwang@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
diff --git a/server/hosts/ssh_host.py b/server/hosts/ssh_host.py
index 130337f..f68269a 100644
--- a/server/hosts/ssh_host.py
+++ b/server/hosts/ssh_host.py
@@ -255,6 +255,8 @@
         return result
 
 
+    @metrics.SecondsTimerDecorator(
+            'chromeos/autotest/ssh/master_ssh_time')
     def run(self, command, timeout=3600, ignore_status=False,
             stdout_tee=utils.TEE_TO_LOGS, stderr_tee=utils.TEE_TO_LOGS,
             connect_timeout=30, options='', stdin=None, verbose=True, args=(),