Change default cirros ssh user

Cirros images allow connection with root and cirros by default.
Interactive sessions for root are not allowed. This will change the
default user to cirros since it allows interactive ssh sessions.

See also https://bugs.launchpad.net/cirros/+bug/1437350

Change-Id: If929ce7a3df944bd17c7f4e3042a6aea0c318b2c
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 2e57007..dcd7e2f 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -668,7 +668,7 @@
 #non_ssh_image_regex = ^.*[Ww]in.*$
 
 # List of user mapped to regex to matching image names. (string value)
-#ssh_user_regex = [["^.*[Cc]irros.*$", "root"]]
+#ssh_user_regex = [["^.*[Cc]irros.*$", "cirros"]]
 
 
 [messaging]