Document Dbh.test_reactive, return saner values

In the FreeSWITCH core, the return value of switch_case_db_test_reactive
is ignored, but it is usable in LUA modules (and other bindings via
SWIG). The LUA API example[1] shows how to check the return value, but
that example miserably fails if the database did not exist before.

Changes:

 - Document the expected behavior of the test_reactive function.
 - Assert that test_sql and sql_reactive are both given. If either
   query is not given, the caller is using the wrong API.
 - When SCF_AUTO_SCHEMAS is cleared, use the return value of the
   test_sql execution. Does anybody use this? Why not remove it?
 - Do not unconditionally return SWITCH_FALSE when test_sql fails,
   instead allow it to become SWITCH_TRUE when reactive_sql passes.
 - Remove the unnecessary test_sql check for SCDB_TYPE_CORE_DB
   (this is now enforced through an assert check). (+reindent)
 - Clarify the error message of drop_sql, prepending "Ignoring" to
   the "SQL ERR" message.
 - LUA: Do not print "DBH NOT Connected" if the query fails. This was
   the initial source of confusion.

 [1]: https://confluence.freeswitch.org/display/FREESWITCH/Lua+API+Reference

src/mod/languages/mod_lua/freeswitch_lua.cpp

@@ -394,9 +394,9 @@ bool Dbh::test_reactive(char *test_sql, char *drop_sql, char *reactive_sql)
     if (switch_cache_db_test_reactive(dbh, test_sql, drop_sql, reactive_sql) == SWITCH_TRUE) {
       return true;
     }
+  } else {
+    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_ERROR, "DBH NOT Connected.\n");
   }
-
-  switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_ERROR, "DBH NOT Connected.\n");
   return false;
 }