tests: check_disk_smb may exit with critical for unresponsive hosts too

Unknown (ex. debian 7)
%> ./check_disk_smb -H 1.1.1.1 -s np_foobar -vvv
/usr/bin/smbclient //1.1.1.1/np_foobar -U guest% -c du
No Answer from Client

Critical (ex. debian 8)
%> ./check_disk_smb -H 1.1.1.1 -s np_foobar -vvv
/usr/bin/smbclient //1.1.1.1/np_foobar -U guest% -c du
Connection to 1.1.1.1 failed
CRITICAL

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>
check_dns: unified check output

this also allows us to make tests against "critical" in the output.

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>