Description of problem:
If '_', [space], '(', ')', '@', etc and non English characters are used in the container's name to search for in the registry, an unexpected error occurs and a traceback is in logs. The error is the same if the entered container's name is alphanumeric (with possible '.', '-' or '/') but doesn't exist in the registry.

Version-Release number of selected component (if applicable):
iso 20161206

How reproducible:
always

Steps to Reproduce:
1. 'ad' add a new Red Hat docker container
2. type 'test' or 'rhel10' when prompted for name of the container in the registry
3. also try names with non alphanumeric characters beside '.', '-' and '/'

Actual results:

>> rhui (repo) => ad

Name of the container in the registry: 
rhel10


An unexpected error has occurred during the last operation.
More information can be found in /root/.rhui/rhui.log.

2016-12-07 07:11:48,022 - <type 'exceptions.NameError'>
2016-12-07 07:11:48,023 - Unexpected error caught at the shell level
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 88, in safe_listen
    self.listen(clear=first_run)
  File "/usr/lib/python2.7/site-packages/rhui/tools/shell.py", line 127, 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/repo.py", line 205, in add_docker
    if docker_utils.is_valid_docker_upstream(upstream_name):
  File "/usr/lib/python2.7/site-packages/rhui/common/docker_utils.py", line 13, in is_valid_docker_upstream
    LOG.debug(_('Failed to connect to upstream registry %s' % url ))
NameError: global name '_' is not defined

>> rhui (repo) => ad

Name of the container in the registry: 
rhel7(rpms)   


An unexpected error has occurred during the last operation.
More information can be found in /root/.rhui/rhui.log.



Expected results:
"There is no such container in the registry."