k8s: Resolve Docker response formatting issue

k8s: Resolve Docker response formatting issue

Checker collects information on cluster by Docker queries:

$ docker ps ARGS...      # Casablanca
$ docker inspect ARGS... # Dublin

Arrays of values are then filtered from those. They include:

* opening bracket ('['),
* closing bracket (']'),
* new line.

Additional characters affect check results if last flag (including
"]\n") requires specific value.

Issue-ID: SECCOM-235
Change-Id: I6838342b7e2ecdc44a47ffe02286266003e0b4d3
Signed-off-by: Pawel Wieczorek <p.wieczorek2@samsung.com>