Remove check_floating_ip_status & _associate_floating_ip methods

As tempest.scenario.manager was announced stable interface
in Tempest 27.0.0[1] it can be now reused in plugins.

Replaced methods:
	* _associate_floating_ip
	* check_floating_ip_status

Etherpad concerning this effort:
https://etherpad.opendev.org/p/tempest-scenario-manager-cleanup

The commit also bumps the minimal version of tempest in the
requirements to tempest>=27.0.0.

[1] https://docs.openstack.org/releasenotes/tempest/v27.0.0.html#release-notes-27-0-0

Change-Id: Ie17c1d9349e98ce016801bf47c1cb9dba18b51f6
diff --git a/requirements.txt b/requirements.txt
index fd67fab..6922d70 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,4 +6,4 @@
 
 ddt>=1.0.1 # MIT
 oslo.log>=3.36.0 # Apache-2.0
-tempest>=17.1.0 # Apache-2.0
+tempest>=27.0.0 # Apache-2.0