Using lb pool to speedup lb creating

[magicsong]

As creating a lb in qingcloud is so slow now, we can create some lbs in advance

[duanjiong]

It costs money to create a load balancer, users are unlikely to be satisfied, and services are not created and removed as often as they should be.

[duanjiong]

/cc @zheng1

[zheng1]

Consider adding a configuration item to let users choose whether to use the LB pool.

This issue is a low priority.