[WFDISC-54] Do not cancel DiscoveryAttempt connection creation if oth…

[tadamski]

…er node has provided the result already

@dmlloyd
I'm opening this PR as a follow up to discussion in #68:

• I have just modified the close method, but I don't believe removing cancellation handlers is appropriate as there possibly may be some other trigger for cancellation and that has to be taken into account
• Removing cancellation fixes the intial problem in WFTC-53
• I have also run wildfly integration tests to double check if this removal causes some unanticipated problem but all seems fine
• I was concerned whether this change may lead to attempts of many connection creation if there are some problems with connection establishment but looking at ClientServiceHandle code imho this should work fine as well.