encoding/xml: format test output using subtests
encoding/xml: format test output using subtests

Change-Id: I2d155c838935cd8427abd142a462ff4c56829715
Reviewed-on: https://go-review.googlesource.com/37948
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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