Tools: autotest: wait_ekf_happy checks status bits rather than value

Based on discussions prompted by @khancyr's PR
https://github.com/ArduPilot/ardupilot/pull/8022

Check that we have bits set we want set and that bits we don't want set
aren't set.  In the future we might take these bit sets as parameters.

Tools/autotest/common.py

@@ -698,7 +698,19 @@ class AutoTest(ABC):
         """Wait for EKF to be happy"""
 
         tstart = self.get_sim_time()
-        required_value = 831
+        # all of these must be set for arming to happen:
+        required_value = (mavutil.mavlink.EKF_ATTITUDE |
+                          mavutil.mavlink.ESTIMATOR_VELOCITY_HORIZ |
+                          mavutil.mavlink.ESTIMATOR_VELOCITY_VERT |
+                          mavutil.mavlink.ESTIMATOR_POS_HORIZ_REL |
+                          mavutil.mavlink.ESTIMATOR_POS_HORIZ_ABS |
+                          mavutil.mavlink.ESTIMATOR_POS_VERT_ABS |
+                          mavutil.mavlink.ESTIMATOR_PRED_POS_HORIZ_REL |
+                          mavutil.mavlink.ESTIMATOR_PRED_POS_HORIZ_ABS)
+        # none of these bits must be set for arming to happen:
+        error_bits = (mavutil.mavlink.ESTIMATOR_CONST_POS_MODE |
+                      mavutil.mavlink.ESTIMATOR_GPS_GLITCH |
+                      mavutil.mavlink.ESTIMATOR_ACCEL_ERROR)
         self.progress("Waiting for EKF value %u" % required_value)
         while timeout is None or self.get_sim_time() < tstart + timeout:
             m = self.mav.recv_match(type='EKF_STATUS_REPORT', blocking=True)
@@ -706,7 +718,11 @@ class AutoTest(ABC):
             if (tstart - self.get_sim_time()) % 5 == 0:
                 self.progress("Wait EKF.flags: required:%u current:%u" %
                               (required_value, current))
-            if current == required_value:
+            errors = current & error_bits
+            if errors:
+                self.progress("Wait EKF.flags: errors=%u" % errors)
+                continue
+            if (current & required_value == required_value):
                 self.progress("EKF Flags OK")
                 return True
         self.progress("Failed to get EKF.flags=%u" % required_value)