Support uploading multiple certificates. [install-interface]

To enable multiple certificates support in certificate manager,
and resolve following issues :

 openbmc/phosphor-certificate-manager#3,
 openbmc/bmcweb#84

the Install method should return a string with dbus path to just
created certificate. It will allow to recognize new certificate
and return proper values in redfish response to certificate POST
method.

Signed-off-by: Zbigniew Kurzynski <zbigniew.kurzynski@intel.com>
Change-Id: I58bfb8a86f56923e7f7aca0d10ed7838537d7c14
diff --git a/xyz/openbmc_project/Certs/Install.interface.yaml b/xyz/openbmc_project/Certs/Install.interface.yaml
index 5fe9c1d..dbbfcd8 100644
--- a/xyz/openbmc_project/Certs/Install.interface.yaml
+++ b/xyz/openbmc_project/Certs/Install.interface.yaml
@@ -12,6 +12,13 @@
               Path of file that contains both the certificate public and
               private key. (Example: a .PEM file containing both signed
               certificate and private key).
+
+      returns:
+        - name: ObjectPath
+          type: string
+          description: >
+              D-Bus object path to created object.
+
       errors:
         - xyz.openbmc_project.Common.Error.InternalFailure
         - xyz.openbmc_project.Common.Error.NotAllowed