ipatests: Perform a connection test before preparing the client

When the host is down, the preparation of the host fails. This
produces misleading errors, since the test framework reports that
the actual command being executed failed, when in fact (in case
of SSHTransport), the cause of failure was unability to establish
a SSH session.

https://fedorahosted.org/freeipa/ticket/4132

Reviewed-By: Nathaniel McCallum <npmccallum@redhat.com>

ipatests/test_integration/tasks.py

@@ -42,6 +42,10 @@ log = log_mgr.get_logger(__name__)
 def prepare_host(host):
     if isinstance(host, Host):
         env_filename = os.path.join(host.config.test_dir, 'env.sh')
+
+        # First we try to run simple echo command to test the connection
+        host.run_command(['true'], set_env=False)
+
         host.collect_log(env_filename)
         host.transport.mkdir_recursive(host.config.test_dir)
         host.put_file_contents(env_filename, env_to_script(host.to_env()))