Increase code coverage for Lua libraries

Add test coverage for lua libraries
Remove dead code in Lua implementation

Signed-off-by: Don Brady <don.brady@delphix.com>

module/lua/lstrlib.c

@@ -174,6 +174,7 @@ static int str_char (lua_State *L) {
 }
 
 
+#if defined(LUA_USE_DUMP)
 static int writer (lua_State *L, const void* b, size_t size, void* B) {
   (void)L;
   luaL_addlstring((luaL_Buffer*) B, (const char *)b, size);
@@ -191,7 +192,7 @@ static int str_dump (lua_State *L) {
   luaL_pushresult(&b);
   return 1;
 }
-
+#endif
 
 
 /*
@@ -992,7 +993,9 @@ static int str_format (lua_State *L) {
 static const luaL_Reg strlib[] = {
   {"byte", str_byte},
   {"char", str_char},
+#if defined(LUA_USE_DUMP)
   {"dump", str_dump},
+#endif
   {"find", str_find},
   {"format", str_format},
   {"gmatch", str_gmatch},