net: add timeout to DNS requests sent by TestSpecialDomainName
net: add timeout to DNS requests sent by TestSpecialDomainName

The timeout means that TestSpecialDomainName will not hang if
the DNS server does not respond to the request.

Fixes #13939

Change-Id: I46e30bbd3c11b6c560656134e704331cf6f8af3f
Reviewed-on: https://go-review.googlesource.com/18661
Reviewed-by: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

suncycheng/go,linux-on-ibm-z/go,binarycrusader/go,nawawi/go,cloudflare/go,Cofyc/go,suncycheng/go,binarycrusader/go,linux-on-ibm-z/go,ImJasonH/go,ganboing/go-esx,nawawi/go,polyverse-security/go,goodlang/good,akutz/go,4ad/go,derekmarcotte/go,CAFxX/go,CAFxX/go,codestation/go,Endika/go,josharian/go,vsekhar/elastic-go,golang/go,polyverse-security/go,binarycrusader/go,josharian/go,miolini/go,vsekhar/elastic-go,mwhudson/go,Samurais/go,4ad/go,ImJasonH/go,Cofyc/go,akutz/go,goodlang/good,akutz/go,nawawi/go,goodlang/good,Samurais/go,sndnvaps/go,ImJasonH/go,mwhudson/go,codestation/go,golang/go,ganboing/go-esx,polyverse-security/go,CAFxX/go,CAFxX/go,miolini/go,nawawi/go,suncycheng/go,vsekhar/elastic-go,goodlang/good,4ad/go,binarycrusader/go,goodlang/good,ganboing/go-esx,linux-on-ibm-z/go,Endika/go,Samurais/go,Cofyc/go,theif519/go,Cofyc/go,binarycrusader/go,Endika/go,ganboing/go-esx,miolini/go,derekmarcotte/go,theif519/go,vsekhar/elastic-go,vanloswang/go,Endika/go,theif519/go,linux-on-ibm-z/go,cloudflare/go,Endika/go,theif519/go,codestation/go,suncycheng/go,nawawi/go,4ad/go,momchil-velikov/go,vanloswang/go,suncycheng/go,ImJasonH/go,Samurais/go,CAFxX/go,vsekhar/elastic-go,ganboing/go-esx,CAFxX/go,akutz/go,josharian/go,derekmarcotte/go,sndnvaps/go,codestation/go,vanloswang/go,theif519/go,mwhudson/go,Cofyc/go,golang/go,codestation/go,josharian/go,mwhudson/go,cyberroadie/go,akutz/go,vsekhar/elastic-go,cloudflare/go,goodlang/good,golang/go,mwhudson/go,sndnvaps/go,mwhudson/go,Endika/go,derekmarcotte/go,binarycrusader/go,sndnvaps/go,akutz/go,Samurais/go,momchil-velikov/go,binarycrusader/go,Endika/go,nawawi/go,derekmarcotte/go,ganboing/go-esx,miolini/go,mwhudson/go,linux-on-ibm-z/go,ganboing/go-esx,josharian/go,goodlang/good,ganboing/go-esx,goodlang/good,miolini/go,CAFxX/go,akutz/go,akutz/go,binarycrusader/go,vanloswang/go,cloudflare/go,theif519/go,polyverse-security/go,cloudflare/go,theif519/go,4ad/go,momchil-velikov/go,miolini/go,Samurais/go,ImJasonH/go,cyberroadie/go,Cofyc/go,suncycheng/go,sndnvaps/go,josharian/go,vsekhar/elastic-go,polyverse-security/go,Cofyc/go,golang/go,miolini/go,vanloswang/go,ImJasonH/go,momchil-velikov/go,cloudflare/go,momchil-velikov/go,mwhudson/go,4ad/go,derekmarcotte/go,sndnvaps/go,golang/go,cloudflare/go,christopher-henderson/Go,josharian/go,codestation/go,4ad/go,derekmarcotte/go,derekmarcotte/go,cyberroadie/go,nawawi/go,cyberroadie/go,Cofyc/go,polyverse-security/go,Endika/go,vsekhar/elastic-go,codestation/go,suncycheng/go,cyberroadie/go,linux-on-ibm-z/go,ImJasonH/go,Samurais/go,momchil-velikov/go,theif519/go,suncycheng/go,momchil-velikov/go,nawawi/go,codestation/go,vanloswang/go,golang/go,cyberroadie/go,sndnvaps/go,cyberroadie/go,Samurais/go,miolini/go,cloudflare/go,linux-on-ibm-z/go,vanloswang/go,sndnvaps/go,CAFxX/go,golang/go,linux-on-ibm-z/go,ImJasonH/go,momchil-velikov/go,polyverse-security/go,4ad/go,josharian/go,polyverse-security/go,vanloswang/go,cyberroadie/go