Description of problem:

- get the following exception when service starts: 

hread-13::DEBUG::2012-02-09 16:03:44,024::utils::601::Storage.Misc.excCmd::(execCmd) SUCCESS: <err> = ''; <rc> = 0
Thread-13::ERROR::2012-02-09 16:03:44,178::BindingXMLRPC::840::vds::(wrapper) Traceback (most recent call last):
  File "/usr/share/vdsm/BindingXMLRPC.py", line 830, in wrapper
    res = f(*args, **kwargs)
  File "/usr/share/vdsm/BindingXMLRPC.py", line 263, in getCapabilities
    ret['info'].update(self.getServerInfo())
  File "/usr/share/vdsm/BindingXMLRPC.py", line 91, in getServerInfo
    'lastClientIface': caps._getIfaceByIP(last) }
  File "/usr/share/vdsm/caps.py", line 231, in _getIfaceByIP
    remote = struct.unpack('I', socket.inet_aton(addr))[0]
error: illegal IP address string passed to inet_aton

the bug here is 'last' == '', then last is passed to getIfaceByIP() and result an error of illegal IP address.