only build test thread_pool_executor_1114_test if HPX_LOCAL_SCHEDULER is set

Hi,

in the current master with default configuration, "make tests" fails.

This is because "thread_pool_executor_1114" requires local_queue_executor, which is disabled if HPX_LOCAL_SCHEDULER is set to false, which is the default. The error message is:

CMakeFiles/thread_pool_executor_1114_test_exe.dir/thread_pool_executor_1114.cpp.o: In function `hpx_startup::user_main()':
thread_pool_executor_1114.cpp:(.text+0xd9e): undefined reference to `hpx::threads::executors::local_queue_executor::local_queue_executor()'

The proposed fix builds thread_pool_executor_1114 only if HPX_LOCAL_SCHEDULER is set to ON