os: clean up after test
os: clean up after test

Noted in CL 31358 after submit.

Change-Id: I76ddad9b9e27dd6a03c1c4f49153213747fe0a61
Reviewed-on: https://go-review.googlesource.com/31365
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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