net/http: deflake TestClientRedirects
net/http: deflake TestClientRedirects

Fix another case of a parallel test relying on a global variable
(DefaultTransport) implicitly.

Use the private Transport already in scope instead. It's closed at the
end, instead of randomly via another test.

Change-Id: I95e51926177ad19a766cabbb306782ded1bbb59b
Reviewed-on: https://go-review.googlesource.com/32913
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

goodlang/good,polyverse-security/go,golang/go,golang/go,polyverse-security/go,codestation/go,linux-on-ibm-z/go,polyverse-security/go,josharian/go,suncycheng/go,Cofyc/go,ImJasonH/go,Cofyc/go,golang/go,vsekhar/elastic-go,akutz/go,josharian/go,codestation/go,derekmarcotte/go,josharian/go,Cofyc/go,derekmarcotte/go,ImJasonH/go,nawawi/go,ImJasonH/go,vsekhar/elastic-go,linux-on-ibm-z/go,cloudflare/go,derekmarcotte/go,vsekhar/elastic-go,derekmarcotte/go,CAFxX/go,goodlang/good,derekmarcotte/go,polyverse-security/go,derekmarcotte/go,Cofyc/go,akutz/go,nawawi/go,vsekhar/elastic-go,vsekhar/elastic-go,vsekhar/elastic-go,codestation/go,golang/go,suncycheng/go,suncycheng/go,akutz/go,golang/go,suncycheng/go,ImJasonH/go,linux-on-ibm-z/go,Cofyc/go,akutz/go,codestation/go,cloudflare/go,ImJasonH/go,linux-on-ibm-z/go,cloudflare/go,codestation/go,polyverse-security/go,linux-on-ibm-z/go,ImJasonH/go,christopher-henderson/Go,suncycheng/go,cloudflare/go,goodlang/good,linux-on-ibm-z/go,cloudflare/go,suncycheng/go,goodlang/good,codestation/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,codestation/go,polyverse-security/go,derekmarcotte/go,nawawi/go,CAFxX/go,josharian/go,linux-on-ibm-z/go,linux-on-ibm-z/go,nawawi/go,Cofyc/go,Cofyc/go,golang/go,suncycheng/go,CAFxX/go,akutz/go,polyverse-security/go,josharian/go,ImJasonH/go,CAFxX/go,polyverse-security/go,Cofyc/go,goodlang/good,vsekhar/elastic-go,vsekhar/elastic-go,nawawi/go,suncycheng/go,akutz/go,josharian/go,nawawi/go,golang/go,josharian/go,cloudflare/go,ImJasonH/go,cloudflare/go,derekmarcotte/go,akutz/go,goodlang/good,CAFxX/go,josharian/go,CAFxX/go,goodlang/good,CAFxX/go,akutz/go,nawawi/go,codestation/go,goodlang/good