Default to m1.micro for heat test flavor.

This is big enough for the current tests, and it may be worth the effort
to optimise more complex tests to fit in a m1.micro for as long as practical.

Change-Id: Id6e43b0b172c996e5091bf2cf7fd245ccfc87d4c
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 3147859..0f60016 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -303,7 +303,7 @@
 
 # Instance type for tests. Needs to be big enough for a
 # full OS plus the test workload
-instance_type = m1.tiny
+instance_type = m1.micro
 
 # Name of heat-cfntools enabled image to use when launching test instances
 # If not specified, tests that spawn instances will not run