phoshor-rsyslog-config: wrap utils::restart

Provide a virtual wrapper around utils::restart in class Server. This
allows mocking in tests.

Change-Id: I79a229eaaaa17860959b8025eb8c152362738acf
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/phosphor-rsyslog-config/server-conf.hpp b/phosphor-rsyslog-config/server-conf.hpp
index 0f67f30..edab113 100644
--- a/phosphor-rsyslog-config/server-conf.hpp
+++ b/phosphor-rsyslog-config/server-conf.hpp
@@ -69,6 +69,10 @@
          */
         virtual uint16_t port(uint16_t value) override;
 
+        /** @brief Restart rsyslog's systemd unit
+         */
+        virtual void restart();
+
     private:
         /** @brief Update remote server address and port in
          *         rsyslog config file.