Replaces use of urlutils with six in policy module

We already have a dependency on six in oslo so having a homegrown
abstraction over urllib doesn't make sense when six already has one.

Change-Id: I38e38321dfb682503a34c0517c928655911fa554
Simplify launch method

Simplify the service launch method to automatically use the lighter
ServiceLauncher if workers is 1 or None.  This makes usage a little
bit simpler.

Change-Id: Ifef48dbf6c62c263cadc7492c1e65b501f58937a
Merge "Simplify launch method"