Description of problem:

When using recent version of atomic on Fedora 25 (atomic-1.15.1-1.fc25.x86_64), `atomic stop $CONTAINER_NAME` raises the following traceback in verbose mode:

{{{
# atomic --debug stop freeipa-server 
Namespace(_class=<class 'Atomic.stop.Stop'>, args=[], assumeyes=False, container='freeipa-server', debug=True, func='stop', opt1=None, opt2=None, opt3=None)
Can't convert 'list' object to str implicitly
Traceback (most recent call last):
  File "/bin/atomic", line 188, in <module>
    sys.exit(_func())
  File "/usr/lib/python3.5/site-packages/Atomic/stop.py", line 40, in stop
    cmd = self.gen_cmd(con_obj.stop_args + self.quote(self.args.args))
TypeError: Can't convert 'list' object to str implicitly

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/bin/atomic", line 210, in <module>
    sys.exit(1)
SystemExit: 1
}}}

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

atomic-1.15.1-1.fc25.x86_64

How reproducible:

Always

Steps to Reproduce:
1. pull container image and install container using atomic
2. run the container using `atomic run`
3. stop the container using atomic stop

Actual results:

Atomic stop stops the running container

Expected results:

The command displays the following error:
TypeError: Can't convert 'list' object to str implicitly

In debug mode the traceback displayed above can be seen.

Additional info:

This seems to be a regression as the command works on my F25 Atomic Host: the version there is atomic-1.13.1-3.git5dfcaa9.fc25.x86_64.