Add work path CLI option (#6922)

Makes it possible to set the work path as a CLI option instead of
relying on environment variables which are somewhat opaque

models/ssh_key_test.go

@@ -14,7 +14,7 @@ import (
 )
 
 func init() {
-	setting.SetCustomPathAndConf("", "")
+	setting.SetCustomPathAndConf("", "", "")
 	setting.NewContext()
 }