Decrease the tempest build interval

Decreasing the build interval leads to faster state change detection,
so it will speed up the gating jobs.

It may increase the possibility of a "hidden" issues causes
indeterministic test results.

Change-Id: Ida5e7296e4ea53d761e0efef34376699337d8377
diff --git a/lib/tempest b/lib/tempest
index a259ee9..aa66ebb 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -44,7 +44,7 @@
 
 NOVA_SOURCE_DIR=$DEST/nova
 
-BUILD_INTERVAL=3
+BUILD_INTERVAL=1
 BUILD_TIMEOUT=400