Wait for floating IP to be DOWN before checking port details

Occasionally test_floatingip_port_details() fails, showing
the floating IP attached port status as 'BUILD'.  Wait for the
status to transition to 'DOWN' before checking other port details,
similar as is done to the fixed IP port's device_id value.

Changed afffected method to use constants for port status as well.

Change-Id: I862115b37c97d5a3cad082d8cd4e7b855ef3f88b
Closes-bug: #1792472
1 file changed