Matches one flavor and one image by default

Changes default in the input-scenario settings to match only
one image and one flavor, to avoid consuming gate time.

Fixes bug 1274628

Change-Id: Ide865012269d3f60250d24443e4f20af263ee021
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 21c8506..8bcf2d3 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -494,7 +494,7 @@
 
 # Matching flavors become parameters for scenario tests
 # (string value)
-#flavor_regex=^m1.(micro|nano|tiny)$
+#flavor_regex=^m1.nano$
 
 # SSH verification in tests is skippedfor matching images
 # (string value)