Corrects error message for ping errors from server behavior

* Modified ServerUnreachable message to return whatever message
  is passed to it
* Modified Windows and Linux clients to pass a full failure message
  rather than just an IP address.

Change-Id: Ifc64b28063b1a3584568711f9ff8e4b77b5be399

cloudcafe/compute/common/clients/remote_instance/linux/linux_client.py

@@ -57,7 +57,9 @@ class LinuxClient(RemoteInstanceClient):
                 break
             time.sleep(retry_interval)
             if int(time.time()) - start >= connection_timeout:
-                raise ServerUnreachable(ip_address)
+                raise ServerUnreachable(
+                    'Could not reach the server at {ip_address}'.format(
+                        ip_address=ip_address))
 
         if key is not None:
             auth_strategy = SSHAuthStrategy.KEY_STRING

cloudcafe/compute/common/clients/remote_instance/windows/windows_client.py

@@ -49,7 +49,9 @@ class WindowsClient(RemoteInstanceClient):
         if not self._is_instance_reachable(
                 ip_address=ip_address, retry_interval=retry_interval,
                 timeout=connection_timeout):
-            raise ServerUnreachable(ip_address)
+            raise ServerUnreachable(
+                'Could not reach the server at {ip_address}'.format(
+                    ip_address=ip_address))
 
         self.ip_address = ip_address
         self.username = username

cloudcafe/compute/common/exceptions.py

@@ -164,8 +164,8 @@ class WinRMConnectionException(Exception):
 
 
 class ServerUnreachable(Exception):
-    def __init__(self, address):
-        self.message = 'Could not reach the server at %s.' % address
+    def __init__(self, message):
+        self.message = message
 
     def __str__(self):
         return repr(self.message)