Issue

CDS addition fails with RHUI.
- RHUA: rhua.example.com
- CDS1: cds1.example.com
- CDS2: cds2.example.com

# rhui-manager
   c   manage content delivery servers (CDS)
     a   register (add) a new CDS instance

rhui (cds) => a
------------------
Prior to registering a CDS, the instance must be provisioned with sshd running.
Hostname of the CDS instance to register:
cds1

Username with SSH access to cds1 and sudo privileges:
root

Absolute path to an SSH private key to log into cds1 as root:
/root/rhui-ca.key 

Checking that instance ports are reachable...

<snip>

Fatal error: local() encountered an error (return code 2) while executing 'nc cds1 22 < /dev/null'
Aborting.
Something happened, check the log file for more information: ~/.rhui/rhui.log

/root/.rhui/rhui.log

2018-07-23 04:36:53,883 - Failed to connect to cds1: local() encountered an error (return code 2) while executing 'nc rcds1 22 < /dev/null'.
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 92, in safe_listen
    self.listen(clear=first_run)
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 131, in listen
    Shell.listen(self)
  File "/usr/lib/python2.7/site-packages/rhui/common/shell.py", line 186, in listen
    item.func(*args, **item.kwargs)
  File "/usr/lib/python2.7/site-packages/rhui/tools/screens/instances.py", line 191, in register
    self._register(new_instance, ssh_policy, force=force)
  File "/usr/lib/python2.7/site-packages/rhui/tools/screens/instances.py", line 219, in _register
    self.check_instance_ports(new_instance)
  File "/usr/lib/python2.7/site-packages/rhui/tools/screens/instances.py", line 458, in check_instance_ports
    host=instance[constants.INSTANCE_HOSTNAME_KEY], message=str(e))
RhuiException: Failed to connect to cds1: local() encountered an error (return code 2) while executing 'nc cds1 22 < /dev/null'.