Prior to sending create request to Octavia, LBaaS driver
verifies that LB is in a stable state by polling LB's 'provisioning_status'
using backoff timer.
A similar method is used also for the delete flow.
Unlike LB creation, rest of Octavia operations are completed usually
after few seconds.
This patch extends LBaaS driver to use 'fast' and 'slow' polling
for the relevant Octavia resources.
Closes-Bug: 1798338
Change-Id: Ie6356955e31a64ad98e5fe71bb659de6ae3f0e03
6acbb7ac4f