Disassociate fip before reuse it

Method get_test_validation_resources reuse same floating
for calls within test. Make sure there is no race between
server delete with floating clean up and assign floating
to new server.

Related-PRODX: PRODX-28576
Change-Id: I32f954efa977f20d8b7d335d499c560ce26dc1be
diff --git a/tempest/api/compute/admin/test_create_server.py b/tempest/api/compute/admin/test_create_server.py
index a3db6cc..1d7c534 100644
--- a/tempest/api/compute/admin/test_create_server.py
+++ b/tempest/api/compute/admin/test_create_server.py
@@ -111,6 +111,11 @@
             servers_client=self.client)
         disks_num = len(linux_client.get_disks().split('\n'))
 
+        # disassociate fip explicitly before use it with new server
+        self.floating_ips_client.disassociate_floating_ip_from_server(
+            validation_resources['floating_ip']['ip'],
+            server_no_eph_disk['id'])
+
         # Explicit server deletion necessary for Juno compatibility
         self.client.delete_server(server_no_eph_disk['id'])