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
1 file changed