Fix bug 576 about ssh keys

Change-Id: I69f73e6ce201e6e46804624271b9183ac2bbfc98
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>
diff --git a/osm_nbi/validation.py b/osm_nbi/validation.py
index 292ec97..6999435 100644
--- a/osm_nbi/validation.py
+++ b/osm_nbi/validation.py
@@ -194,7 +194,7 @@
         "nsDescription": {"oneOf": [description_schema, {"type": "null"}]},
         "nsdId": id_schema,
         "vimAccountId": id_schema,
-        "ssh_keys": {"type": "string"},
+        "ssh_keys": {"type": "array", "items": {"type": "string"}},
         "nsr_id": id_schema,
         "vnf": {
             "type": "array",