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/msc_osmo.py b/src/osmo_gsm_tester/obj/msc_osmo.py
index cb8894f..048934e 100644
--- a/src/osmo_gsm_tester/obj/msc_osmo.py
+++ b/src/osmo_gsm_tester/obj/msc_osmo.py
@@ -21,8 +21,15 @@
 import pprint
 
 from ..core import log, util, config, template, process
+from ..core import schema
 from . import osmo_ctrl, pcap_recorder, smsc
 
+def on_register_schemas():
+    resource_schema = {
+        'path': schema.STR,
+        }
+    schema.register_resource_schema('modem', resource_schema)
+
 class OsmoMsc(log.Origin):
 
     def __init__(self, suite_run, hlr, mgw, stp, ip_address):