Generate schemas dynamically from pieces provided by each object class

This way we benefit from:
* knowing which attributes are used/required by each object class and
  subclass
* Having validation function definitions near the class going to use them

Change-Id: I8fd6773c51d19405a585977af4ed72cad2b21db1
diff --git a/src/osmo_gsm_tester/obj/enb_srs.py b/src/osmo_gsm_tester/obj/enb_srs.py
index 243ffaa..0816ca6 100644
--- a/src/osmo_gsm_tester/obj/enb_srs.py
+++ b/src/osmo_gsm_tester/obj/enb_srs.py
@@ -24,6 +24,14 @@
 from . import enb
 from . import rfemu
 
+from ..core import schema
+
+def on_register_schemas():
+    config_schema = {
+        'enable_pcap': schema.BOOL_STR,
+        }
+    schema.register_config_schema('enb', config_schema)
+
 def rf_type_valid(rf_type_str):
     return rf_type_str in ('zmq', 'uhd', 'soapy', 'bladerf')