Make log level INFO in addTrustedCACertFile()

With WARN level, they will be always printed on Mac OS and old GNUTLS
build which does not have its API.

src/AppleTLSContext.cc

@@ -54,7 +54,7 @@ bool AppleTLSContext::addCredentialFile(const std::string& certfile,
 
 bool AppleTLSContext::addTrustedCACertFile(const std::string& certfile)
 {
-  A2_LOG_WARN("TLS CA bundle files are not supported. Use the KeyChain to manage your certificates.");
+  A2_LOG_INFO("TLS CA bundle files are not supported. Use the KeyChain to manage your certificates.");
   return false;
 }
 

src/LibgnutlsTLSContext.cc

@@ -114,7 +114,7 @@ bool GnuTLSContext::addSystemTrustedCACerts()
     return true;
   }
 #else
-  A2_LOG_WARN("System certificates not supported");
+  A2_LOG_INFO("System certificates not supported");
   return false;
 #endif
 }