Move name of DB superuser to a macro

To ensure the superuser role name ("dba") is used consistently, it is
now defined as the macro DB_SUPERUSER_ROLE.

src/manage_pg.c

@@ -38,6 +38,11 @@
  */
 #define G_LOG_DOMAIN "md manage"
 
+/**
+ * @brief Database superuser role
+ */
+#define DB_SUPERUSER_ROLE "dba"
+
 
 /* Headers */
 int
@@ -197,7 +202,7 @@ manage_create_sql_functions ()
 
   /* Functions in C. */
 
-  sql ("SET role dba;");
+  sql ("SET ROLE \"%s\";", DB_SUPERUSER_ROLE);
 
   sql ("CREATE OR REPLACE FUNCTION hosts_contains (text, text)"
        " RETURNS boolean"
@@ -3076,7 +3081,7 @@ check_db_extensions ()
       g_debug ("%s: All required extensions are available.", __func__);
 
       // Switch to superuser role and try to install extensions.
-      sql ("SET ROLE dba;");
+      sql ("SET ROLE \"%s\";", DB_SUPERUSER_ROLE);
 
       sql ("CREATE EXTENSION IF NOT EXISTS \"uuid-ossp\"");
       sql ("CREATE EXTENSION IF NOT EXISTS \"pgcrypto\"");