Fix bug #1077 slice instantiation with ssh_keys option

Change-Id: Ied5223046f00b630442043f3e6ecd34f6867c24f
Signed-off-by: Felipe Vicens <felipe.vicens@atos.net>
diff --git a/osm_nbi/validation.py b/osm_nbi/validation.py
index 6a483f3..505201c 100644
--- a/osm_nbi/validation.py
+++ b/osm_nbi/validation.py
@@ -958,7 +958,7 @@
         "nstId": string_schema,
         "vimAccountId": id_schema,
         "timeout_nsi_deploy": integer1_schema,
-        "ssh_keys": {"type": "string"},
+        "ssh_keys": {"type": "array", "items": {"type": "string"}},
         "nsi_id": id_schema,
         "additionalParamsForNsi": object_schema,
         "netslice-subnet": {