ncm-sysconfig: Update and clarify schema

* Break apart schema into sub-types for clarification
* Disallow empty values
* Make use of schema in tests
* Add annotations based on paraphrased description from pod.

ncm-sysconfig/src/main/pan/components/sysconfig/schema.pan

@@ -2,16 +2,34 @@
 # ${developer-info}
 # ${author-info}
 
-
 declaration template components/sysconfig/schema;
 
 include 'quattor/schema';
 
+@documentation{
+Contents of a sysconfig file modelled as a dict of key-value pairs.
+
+Two reserved keys `prologue` and `epilogue` are treated specially,
+their values will be copied verbatim into the file before or after the key-pair definitions.
+
+Example:
+
+'/software/components/sysconfig/files/scfg' = dict(
+    'epilogue', 'export LANG=C',
+    'KEY', 'VALUE',
+);
+
+This will create the file `/etc/sysconfig/scfg` which contains:
+
+KEY=VALUE
+export LANG=C
+}
+type component_sysconfig_file = string(1..){};
+
 type component_sysconfig = {
     include structure_component
-    'files' ? string{}{}
+    @{ dict of dicts with a file name as the first key and the contents of each file as the child dict. }
+    'files' ? component_sysconfig_file{}
 };
 
 bind '/software/components/sysconfig' = component_sysconfig;
-
-

ncm-sysconfig/src/test/resources/configure.pan

@@ -1,5 +1,7 @@
 object template configure;
 
+include 'components/sysconfig/schema';
+
 prefix '/software/components/sysconfig';
 
 'files/examplefile/key1' = 'testvalue';