api: don't reuse mgo sessions on tests
api: don't reuse mgo sessions on tests

Trying to fix tsuru-race build :-)

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