Change InternalFailure to NotAllowed for replace

This patch is about using NotAllowed instead of InternalFailure for
certificate replacement routine. Currently there is a check to prevent
replacing current certificate with certificate with subject/issuer
already existing on the certificate list (currently replacing
certificate is not taken into account). And for that case it makes
sense to use NotAllowed error instead of InternalFailure.

Tested by replacing one of the currently available certificates with
new one with subject/issuer the same as one of the currently available
certificate.

Signed-off-by: Zbigniew Lukwinski <zbigniew.lukwinski@linux.intel.com>
Change-Id: Ia480e8fe9b70ba7f0291541f47e78680f48a3646
diff --git a/certs_manager.cpp b/certs_manager.cpp
index 2391267..2d1afed 100644
--- a/certs_manager.cpp
+++ b/certs_manager.cpp
@@ -204,8 +204,11 @@
     }
     else
     {
-        log<level::ERR>("Certificate already exist");
-        elog<InternalFailure>();
+        using NotAllowed =
+            sdbusplus::xyz::openbmc_project::Common::Error::NotAllowed;
+        using Reason = xyz::openbmc_project::Common::NotAllowed::REASON;
+
+        elog<NotAllowed>(Reason("Certificate already exist"));
     }
 }