Adds instance_utils library and initial SSH tests

* Provides an instance util class for common server queries
* Refactored the create server smoke test as an example
* Added ssh tag to tests requiring SSH to allow them to be
  skipped if needed

Change-Id: Ia34d7c75ad05f7658d1abb7bebeb1bbd271fd089
diff --git a/tempest/exceptions.py b/tempest/exceptions.py
index b49e9e6..f7717d5 100644
--- a/tempest/exceptions.py
+++ b/tempest/exceptions.py
@@ -75,3 +75,12 @@
 
 class Duplicate(TempestException):
     message = "An object with that identifier already exists"
+
+
+class SSHTimeout(TempestException):
+    message = ("Connection to the %(host)s via SSH timed out.\n"
+                "User: %(user)s, Password: %(password)s")
+
+
+class ServerUnreachable(TempestException):
+    message = "The server is not reachable via the configured network"