Set aodh_threshold to "6000000000" in tempest.conf

For autoscaling granularity is set to 60 and the heat
stack is expected to scale out after instance reaches
CPU utilization higher than 10%.

According to this configuration the cpu time must be
10**9*60*(10/100) which is 6000000000 ns.

The default threshold for aodh alarms is "10000000"
which comes from ceilometer's devstack settings.

This change overrides the aodh_threshold value in
tempest.conf to the correct cpu time as per
cpu util and granularity values.

Signed-off-by: Yadnesh Kulkarni <ykulkarn@redhat.com>
Change-Id: Ic90613b70556d0ce5bcf64c2305a3351928bf83e

.zuul.yaml

@@ -37,6 +37,7 @@
         CEILOMETER_BACKEND: "gnocchi"
         CEILOMETER_PIPELINE_INTERVAL: 15
         USE_PYTHON3: False
+        CEILOMETER_ALARM_THRESHOLD: 6000000000
       devstack_local_conf:
         test-config:
           $TEMPEST_CONFIG:
@@ -90,6 +91,7 @@
         GNOCCHI_ARCHIVE_POLICY_TEMPEST: "ceilometer-high-rate"
         CEILOMETER_BACKEND: "gnocchi"
         CEILOMETER_PIPELINE_INTERVAL: 15
+        CEILOMETER_ALARM_THRESHOLD: 6000000000
       devstack_local_conf:
         test-config:
           $TEMPEST_CONFIG: