membase-cli should have nicer error msg when talking to a down cluster

if the northscale server is down or stopped, and you try to use the membase-cli, you get an ugly python error msg.

I would instead expect to see something like...

ERROR: blah blah some nice err msg

Here's what's there for 1.6.0a-39...

[root@Config85VM0 1.6.0a]# ./bin/cli/membase server-list -c 127.0.0.1:8080
Traceback (most recent call last):
File "./bin/cli/membase", line 101, in ?
main()
File "./bin/cli/membase", line 98, in main
taskrunner.runCmd(cmd, server, port, user, password, opts)
File "/opt/NorthScale/1.6.0a/bin/cli/listservers.py", line 56, in runCmd
password)
File "/opt/NorthScale/1.6.0a/bin/cli/listservers.py", line 83, in getData
password)
File "/opt/NorthScale/1.6.0a/bin/cli/restclient.py", line 91, in sendCmd
self.bootStrap(headers)
File "/opt/NorthScale/1.6.0a/bin/cli/restclient.py", line 58, in bootStrap
self.conn.request('GET', '/pools','',headers)
File "/usr/lib64/python2.4/httplib.py", line 810, in request
self._send_request(method, url, body, headers)
File "/usr/lib64/python2.4/httplib.py", line 833, in _send_request
self.endheaders()
File "/usr/lib64/python2.4/httplib.py", line 804, in endheaders
self._send_output()
File "/usr/lib64/python2.4/httplib.py", line 685, in _send_output
self.send(msg)
File "/usr/lib64/python2.4/httplib.py", line 652, in send
self.connect()
File "/usr/lib64/python2.4/httplib.py", line 636, in connect
raise socket.error, msg
socket.error: (111, 'Connection refused')