api/auth: using os.Stat instead of os.Open
api/auth: using os.Stat instead of os.Open

If we just want to check if the file exists, Stat is way faster than
Open.

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