Fix stporch init exception (#3449)

What I did
Fixed stporch init exception
Why I did it
SAI retrieval of STP attributes may return either SAI_STATUS_NOT_SUPPORTED or SAI_STATUS_NOT_IMPLEMENTED. An exception has been added to handle such failures, preventing Orchagent from starting on systems where STP is not supported

orchagent/stporch.cpp

@@ -20,6 +20,7 @@ StpOrch::StpOrch(DBConnector * db, DBConnector * stateDb, vector<string> &tableN
 
     sai_attribute_t attr;
     sai_status_t status;
+    bool ret = false;
 
     m_stpTable = unique_ptr<Table>(new Table(stateDb, STATE_STP_TABLE_NAME));
 
@@ -28,12 +29,13 @@ StpOrch::StpOrch(DBConnector * db, DBConnector * stateDb, vector<string> &tableN
     attrs.push_back(attr);
 
     status = sai_switch_api->get_switch_attribute(gSwitchId, (uint32_t)attrs.size(), attrs.data());
-    if (status != SAI_STATUS_SUCCESS)
+    if (status == SAI_STATUS_SUCCESS)
     {
-        throw runtime_error("StpOrch initialization failure");
+	    m_defaultStpId = attrs[0].value.oid;
+	    ret = true;
     }
-    
-    m_defaultStpId = attrs[0].value.oid;
+
+    SWSS_LOG_NOTICE("StpOrch initialization %s", (ret == true)?"success":"failure");
 };