Added prefix parameter to the vmpooler configuration

vmpooler.yaml.example

@@ -161,6 +161,9 @@
 #
 #   - domain
 #     If set, returns a top-level 'domain' JSON key in POST requests
+#
+#   - prefix
+#     If set, prefixes all created VMs with this string.
 
 # Example:
 
@@ -176,6 +179,7 @@
     - 'created_by'
     - 'project'
   domain: 'company.com'
+  prefix: ''
 
 # :pools:
 #