lock_machine: shout when our `swarming` command dies

When I tried to run crosperf without proper `swarming.py`
authentication, crosperf said the machine I wanted to use wasn't
available in skylab. It'd be better if we reported that we couldn't tell
if the machine was/wasn't in skylab due to the tool we're using failing.

Looks like this script can fail for a number of other reasons, too, so
throwing our hands up is likely going to often be our best bet.

BUG=None
TEST=ran without auth; exception was thrown. ran with; things worked.

Change-Id: I4d0e4ec70eddb3a7836686eef819e6175a730756
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2177063
Reviewed-by: Bob Haarman <inglorion@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/lock_machine.py b/lock_machine.py
index 8588ebfd..dc494142 100755
--- a/lock_machine.py
+++ b/lock_machine.py
@@ -386,7 +386,11 @@ class LockManager(object):
            (swarming,
             credential,
             machine.rstrip('.cros')))
-    ret_tup = self.ce.RunCommandWOutput(cmd)
+    exit_code, stdout, stderr = self.ce.RunCommandWOutput(cmd)
+    if exit_code:
+      raise ValueError(
+          'Querying bots failed (2); stdout: %r; stderr: %r' % (stdout, stderr))
+
     # The command will return a json output as stdout. If machine not in skylab
     # stdout will look like this:
     #  {
@@ -395,10 +399,7 @@ class LockManager(object):
     #  }
     # Otherwise there will be a tuple starting with 'items', we simply detect
     # this keyword for result.
-    if 'items' not in ret_tup[1]:
-      return False
-    else:
-      return True
+    return 'items' in stdout
 
   def LeaseSkylabMachine(self, machine):
     """Run command to lease dut from skylab.