api/app: avoid data race between app.Get and env agent on handler tests
api/app: avoid data race between app.Get and env agent on handler tests

The data races were detected by `go test -race` on api/app.

gwmoura/tsuru,Endika/tsuru,tuxmonteiro/tsuru,guilhermebr/tsuru,ArxdSilva/tsuru,tsuru/tsuru,Endika/tsuru,cezarsa/tsuru,ggarnier/tsuru,mderaldo/tsuru,tuxmonteiro/tsuru,hcxiong/tsuru,Endika/tsuru,guilhermebr/tsuru,firebitsbr/tsuru,guilhermebr/tsuru,ggarnier/tsuru,gciotta/tsuru,mderaldo/tsuru,gciotta/tsuru,ggarnier/tsuru,jblancett/tsuru,kgrvamsi/tsuru,cgvarela/tsuru,gwmoura/tsuru,cgvarela/tsuru,hcxiong/tsuru,ggarnier/tsuru,gwmoura/tsuru,4eek/tsuru,tsuru/tsuru,mderaldo/tsuru,ArxdSilva/tsuru,4eek/tsuru,jblancett/tsuru,tsuru/tsuru,hugoantunes/tsuru,kgrvamsi/tsuru,cezarsa/tsuru,tuxmonteiro/tsuru,ArxdSilva/tsuru,tsuru/tsuru,firebitsbr/tsuru,guilhermebr/tsuru,jblancett/tsuru,cgvarela/tsuru,ArxdSilva/tsuru,firebitsbr/tsuru,RichardKnop/tsuru,RichardKnop/tsuru,cezarsa/tsuru,gciotta/tsuru,hcxiong/tsuru,RichardKnop/tsuru,cezarsa/tsuru,4eek/tsuru,kgrvamsi/tsuru,hugoantunes/tsuru