autotest: fix Clamp test altitude bounds for datum reset

The Clamp test checks that a clamped vehicle stays near ground level.
With the height datum reset on arming, altitude is zeroed and baro
noise can put it slightly negative (-0.01m). Change the lower bound
from 0 to -1 to accommodate this.

Author: andyp1per

Tools/autotest/arducopter.py

@@ -14408,7 +14408,7 @@ def Clamp(self):
         self.wait_statustext("SITL: Clamp: grabbed vehicle", check_context=True)
         self.arm_vehicle()
         self.set_rc(3, 2000)
-        self.wait_altitude(0, 5, minimum_duration=5, relative=True)
+        self.wait_altitude(-1, 5, minimum_duration=5, relative=True)
         self.run_cmd(mavutil.mavlink.MAV_CMD_DO_SET_SERVO, p1=11, p2=1000)
         self.wait_statustext("SITL: Clamp: released vehicle", check_context=True)
         self.wait_altitude(5, 5000, minimum_duration=1, relative=True)
@@ -14424,7 +14424,7 @@ def Clamp(self):
         self.wait_statustext("SITL: Clamp: grabbed vehicle", check_context=True)
         self.arm_vehicle()
         self.set_rc(3, 2000)
-        self.wait_altitude(0, 1, minimum_duration=5, relative=True)
+        self.wait_altitude(-1, 1, minimum_duration=5, relative=True)
         self.run_cmd(mavutil.mavlink.MAV_CMD_DO_SET_SERVO, p1=11, p2=1000)
         self.wait_statustext("SITL: Clamp: released vehicle", check_context=True)
         self.wait_altitude(5, 5000, minimum_duration=1, relative=True)