Reduce 'min_compute_nodes' to '2'

It is enought to use 2 compute nodes for tempest scenario tests.

Related-Bug:#PROD-25353

Change-Id: I8f1d165b5d76a119b35c6df9bd1fdb0339a33d00
diff --git a/tempest/tempest_ext.conf b/tempest/tempest_ext.conf
index 856f443..ad6d952 100644
--- a/tempest/tempest_ext.conf
+++ b/tempest/tempest_ext.conf
@@ -6,7 +6,7 @@
 min_microversion = 2.1
 max_microversion = latest
 volume_device_name = vdc
-min_compute_nodes = 3
+min_compute_nodes = 2
 endpoint_type = publicURL
 ping_timeout = 20
 ping_count = 5