scheduler: active_process_percentage goes Float'ing.

BUG=None.
TEST=local scheduler run doesn't throw anymore.

Change-Id: I5df0eb94d46c665100713c34e56b1772d1469b99
Reviewed-on: https://chromium-review.googlesource.com/422394
Commit-Ready: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/scheduler/drone_manager.py b/scheduler/drone_manager.py
index fb0aad2..b296b65 100644
--- a/scheduler/drone_manager.py
+++ b/scheduler/drone_manager.py
@@ -432,7 +432,7 @@
             percent = float(drone.active_processes) / drone.max_processes
         except ZeroDivisionError:
             percent = 100
-        metrics.Gauge('chromeos/autotest/drone/active_process_percentage'
+        metrics.Float('chromeos/autotest/drone/active_process_percentage'
                       ).set(percent, fields={'drone_hostname': drone.hostname})
 
     def trigger_refresh(self):