tests: Disable the OAUTHBEARER tests when using a non-default port number

Tests 842, 843, 844, 845, 887, 888, 889, 890, 946, 947, 948 and 949 fail
if a custom port number is specified via the -b option of runtests.pl.

Suggested by: Kamil Dudka
Bug: http://curl.haxx.se/mail/lib-2015-12/0003.html