[moblab] Use the is_reboot_needed value correctly

Use the return code from --is_reboot_needed correctly
to cause the moblab device to update when a new
version is downloaded and ready to install

BUG=chromium:613747
TEST=updated local moblab device from 10176.62.0 to 10176.65.0 via UI

Change-Id: I2204b3fcf2a2602b72350d380d3112a47a48a2ad
Reviewed-on: https://chromium-review.googlesource.com/895905
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
diff --git a/frontend/afe/moblab_rpc_interface_unittest.py b/frontend/afe/moblab_rpc_interface_unittest.py
index 484a666..87dc346 100644
--- a/frontend/afe/moblab_rpc_interface_unittest.py
+++ b/frontend/afe/moblab_rpc_interface_unittest.py
@@ -496,9 +496,8 @@
         self.mox.StubOutWithMock(moblab_rpc_interface.subprocess, 'check_call')
         moblab_rpc_interface.subprocess.check_call(['sudo',
                 update_engine_client, '--update'])
-        error = moblab_rpc_interface.subprocess.CalledProcessError(2, '')
         moblab_rpc_interface.subprocess.check_call(['sudo',
-                update_engine_client, '--is_reboot_needed']).AndRaise(error)
+                update_engine_client, '--is_reboot_needed'])
 
         self.mox.StubOutWithMock(moblab_rpc_interface.subprocess, 'call')
         moblab_rpc_interface.subprocess.call(['sudo', update_engine_client,