Fixes LP Bug#953450 - Remove vestigial ssh_timeout

AttributeError was occurring in ImageMetadataTest due
to old unused ssh_timeout config value

Change-Id: I25b0d2c7558cd7cd56fad26d766e16e1906cb4f2
diff --git a/tempest/tests/test_image_metadata.py b/tempest/tests/test_image_metadata.py
index 50d4182..bf8b509 100644
--- a/tempest/tests/test_image_metadata.py
+++ b/tempest/tests/test_image_metadata.py
@@ -15,7 +15,6 @@
         cls.config = cls.os.config
         cls.image_ref = cls.config.compute.image_ref
         cls.flavor_ref = cls.config.compute.flavor_ref
-        cls.ssh_timeout = cls.config.nova.ssh_timeout
 
         name = rand_name('server')
         resp, server = cls.servers_client.create_server(name, cls.image_ref,