Fix update_schemas.py to add Oem JsonSchemas

GET on redfish/v1/JsonSchema does not show OEM schemas but shows only
DMTF redfish schemas.

It is because Oem schemas are not included into `schemas.hpp`.

In addition, the explicit OEM JsonSchema gives the content of the file
rather than the valid Json output.

Tested:

- Query JsonSchemas

```
curl -k -H "X-Auth-Token: $token" -X GET "https://$bmc/redfish/v1/JsonSchemas"

curl -k -H "X-Auth-Token: $token" -X GET "https://$bmc/redfish/v1/JsonSchemas/<OemSchema>"
e.g.
curl -k -H "X-Auth-Token: $token" -X GET "https://$bmc/redfish/v1/JsonSchemas/OemManager"
```

- Redfish Service Validator passed

Change-Id: I0fc9c3d4a48fb9c6ddec9591af12fd2c849331e3
Signed-off-by: Myung Bae <myungbae@us.ibm.com>
diff --git a/redfish-core/include/schemas.hpp b/redfish-core/include/schemas.hpp
index fa3143d..0d47c6f 100644
--- a/redfish-core/include/schemas.hpp
+++ b/redfish-core/include/schemas.hpp
@@ -126,5 +126,9 @@
         "UpdateService",
         "VirtualMedia",
         "VirtualMediaCollection",
+        "OemManager",
+        "OemComputerSystem",
+        "OemVirtualMedia",
+        "OpenBMCAccountService",
     };
 }