Set max_microversion 2.42 for hosts tests

The compute os-hosts API is deprecated as of the 2.43 microversion,
so we should set max_microversion = '2.42' for hosts tests.

ref:
https://developer.openstack.org/api-ref/compute/#list-hosts

Change-Id: Icc320de1fac272c8973edada7a556079b3dbf5a7
diff --git a/tempest/api/compute/admin/test_hosts.py b/tempest/api/compute/admin/test_hosts.py
index 00f3256..c246685 100644
--- a/tempest/api/compute/admin/test_hosts.py
+++ b/tempest/api/compute/admin/test_hosts.py
@@ -20,6 +20,8 @@
 class HostsAdminTestJSON(base.BaseV2ComputeAdminTest):
     """Tests hosts API using admin privileges."""
 
+    max_microversion = '2.42'
+
     @classmethod
     def setup_clients(cls):
         super(HostsAdminTestJSON, cls).setup_clients()
diff --git a/tempest/api/compute/admin/test_hosts_negative.py b/tempest/api/compute/admin/test_hosts_negative.py
index 5bd8104..8a91ae2 100644
--- a/tempest/api/compute/admin/test_hosts_negative.py
+++ b/tempest/api/compute/admin/test_hosts_negative.py
@@ -20,6 +20,8 @@
 class HostsAdminNegativeTestJSON(base.BaseV2ComputeAdminTest):
     """Tests hosts API using admin privileges."""
 
+    max_microversion = '2.42'
+
     @classmethod
     def setup_clients(cls):
         super(HostsAdminNegativeTestJSON, cls).setup_clients()