Have only one YAML message header.

util/vpc-tools/abbey.py

@@ -316,10 +316,12 @@ EOF
 fi
 
 cat << EOF >> $extra_vars
+---
 # extra vars passed into
 # abbey.py including versions
 # of all the repositories
 {extra_vars_yml}
+
 {git_refs_yml}
 
 # path to local checkout of
@@ -637,7 +639,7 @@ if __name__ == '__main__':
             extra_vars_yml = f.read()
             extra_vars = yaml.load(extra_vars_yml)
     else:
-        extra_vars_yml = "---\n"
+        extra_vars_yml = ""
         extra_vars = {}
 
     if args.refs:
@@ -645,7 +647,7 @@ if __name__ == '__main__':
             git_refs_yml = f.read()
             git_refs = yaml.load(git_refs_yml)
     else:
-        git_refs_yml = "---\n"
+        git_refs_yml = ""
         git_refs = {}
 
     if args.secure_vars: