ceph-disk: add missing spaces around operator

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph-disk: fix undefined variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph-disk: cast output of _check_output()

Cast output of _check_output() to str() to be able to use
str.split().

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph-disk: remove unnecessary semicolons

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #319 from dalgaaf/wip-da-pylint-3

Fix some smaller Python issues