Path fix for memcachetest script

While trying to track down MB-8083, found issue with memcachetest path...

  http://qa.sc.couchbase.com/job/ubuntu_x64--47_01--connection-P1_DELETE/45/consoleFull

  2014-05-21 23:06:39 | ERROR | MainProcess | test_thread | [remote_util.log_command_output]
    bash: line 0: cd: /tmp//memcachetest: No such file or directory

So, this change removes an extra '/'.

Change-Id: I47c3f22192e3dbc7b44883f540069bd16dacdf80
Reviewed-on: http://review.couchbase.org/37461
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>