Update key usage logic
Update key usage logic

* Move to one place for both code paths
* Assign ExtKeyUsageAny to CA certs to help with validation with the
  Windows Crypto API and Go's validation logic

Fixes #846

hashbrowncipher/vault,kenbreeman/vault,cimarron-pistoncloud/vault,memory/vault,kingland/vault,mgk/vault,joelthompson/vault,kingland/vault,wjam/vault,careyblack/vault,quixoten/vault,danielsomerfield/vault,jgcallero/vault,jmhardison/vault,mymercurialsky/vault,MonsantoCo/vault,hartsock/vault,hartsock/vault,kenbreeman/vault,andrewstuart/vault,hashbrowncipher/vault,geckoboard/vault,tallpauley/vault,Caiyeon/vault,hashicorp/vault,joelthompson/vault,mhurne/vault,naunga/vault,Banno/vault,quixoten/vault,cimarron-pistoncloud/vault,hashicorp/vault,sepiroth887/vault,geckoboard/vault,doubledutch/vault,kingland/vault,grunzwei/vault,grunzwei/vault,sepiroth887/vault,andrewstuart/vault,rnaveiras/vault,kingland/vault,michaelansel/vault,skippy/vault,jmhardison/vault,doodles526/vault,rnaveiras/vault,jmhardison/vault,jmhardison/vault,naunga/vault,doubledutch/vault,mgk/vault,ryon/vault,Aloomaio/vault,chrishoffman/vault,geckoboard/vault,Banno/vault,andrewstuart/vault,jgcallero/vault,lemondrank/vault,grunzwei/vault,jmhardison/vault,annanay25/vault,MonsantoCo/vault,hashbrowncipher/vault,tallpauley/vault,skippy/vault,lirao/vault,wjam/vault,hashicorp/vault,hartsock/vault,rnaveiras/vault,sepiroth887/vault,grunzwei/vault,geckoboard/vault,joelthompson/vault,andrewstuart/vault,careyblack/vault,jam-pot/vault,sepiroth887/vault,memory/vault,careyblack/vault,kingland/vault,lirao/vault,mgk/vault,deverton/hashicorp-vault,peteryhwong/vault,annanay25/vault,hashicorp/vault,rnaveiras/vault,quixoten/vault,doubledutch/vault,mymercurialsky/vault,mhurne/vault,careyblack/vault,hashicorp/vault,doodles526/vault,hartsock/vault,annanay25/vault,ryon/vault,martin-ducar-gd/vault,geckoboard/vault,quixoten/vault,kenbreeman/vault,Aloomaio/vault,deverton/hashicorp-vault,jam-pot/vault,hashicorp/vault,hartsock/vault,mgk/vault,danielsomerfield/vault,martin-ducar-gd/vault,kenbreeman/vault,grunzwei/vault,Caiyeon/vault,LolalyLuo/vault,Aloomaio/vault,LolalyLuo/vault,chrishoffman/vault,andrewstuart/vault,hashbrowncipher/vault,joelthompson/vault,annanay25/vault,doubledutch/vault,Aloomaio/vault,annanay25/vault,lemondrank/vault,rnaveiras/vault,kenbreeman/vault,sepiroth887/vault,careyblack/vault,hashbrowncipher/vault,peteryhwong/vault,doubledutch/vault,michaelansel/vault