Add RemoteClient under tempest.lib

remote_client under tempest.common is used in many projects but the
module is not defined as stable. This patch adds the essential part
of the module into tempest.lib as stable interface.

Change-Id: Idb2206c239f25bc8b8530275e84c834233b9544b
diff --git a/releasenotes/notes/add-tempest-lib-remote-client-adbeb3f42a36910b.yaml b/releasenotes/notes/add-tempest-lib-remote-client-adbeb3f42a36910b.yaml
new file mode 100644
index 0000000..c21751b
--- /dev/null
+++ b/releasenotes/notes/add-tempest-lib-remote-client-adbeb3f42a36910b.yaml
@@ -0,0 +1,10 @@
+---
+features:
+  - Add remote_client under tempest.lib.
+    This remote_client under tempest.lib is defined as stable
+    interface, and now this module provides the following
+    essential methods.
+
+      * exec_command
+      * validate_authentication
+      * ping_host