check_oracle: --tns bad string matching

check_oracle in the 1.4.15 release doesn't correctly parse the output gotten
from at least Oracle 11 (with german locales). I guess it's probably more.
Also it completely needlessly uses sed where basic bash string parsing actually
does more than suffice (and does not run into possible problems with locales
like sed ;)).
--
Just turning attached patch of github issue #1015 into a push request.
(Closes #1015)