Use new http session for every package doc upload
Use new http session for every package doc upload

Before this patch we would use a single http session for the entire doc builder
execution. However, since doc building can take quite a long time this would
cause long periods of inactivity, resulting in a 
  
  <socket: 3> resource vanished

error. To avoid this, we now use a http session every time we upload: so, we
build docs, use a new http session to upload the docs, repeat. This seems to be
a lot more reliable.


dzackgarza/hackage-server,agrafix/hackage-server,tkvogt/hackage-server,edsko/hackage-server,edsko/hackage-server,erantapaa/hackage-server,haskell-infra/hackage-server,snoyberg/hackage-server,erantapaa/hackage-server,tkvogt/hackage-server,grayjay/hackage-server,ocharles/hackage-server,agrafix/hackage-server,chrisdotcode/hackage-server,grayjay/hackage-server,snoyberg/hackage-server,dzackgarza/hackage-server,ocharles/hackage-server,chrisdotcode/hackage-server