Wrapper builder

@aranhoide Big thanks for your help on this one!

To keep the change simple, I ended up using the existing scheme whereby the cloudmaster distributes work to the VMs that do the building, but instead of having it distribute to fallbacks, it now distributes to the wrapper_builder VMs.  Part of why I did this is that the messages for requesting install wrappers come in on the same queue that the cloudmaster uses for handling other things like launching, and I didn't want to have to break out a new queue and update the controller to send to it.  Probably not a huge thing, but one step at a time, right?

I've logged bugs for the follow-on work:

https://github.com/getlantern/lantern_aws/issues/23
https://github.com/getlantern/lantern_aws/issues/24

I tested in my oxctrl3 environment that inviting a new user results in the wrapper builder being run on one of the new wrapper_builder machines, with the final log messages in upload_wrappers.log showing the below:

```
2014-05-15 14:33:45,652 INFO     Uploading wrapper to 2Dh.rjQ7RMdSLopdoVbTK_qF2MHcvobbAVR0nBRohNyk2oUtSJxmdpo5fI8c6hlZ~mLkt1Ne8lN_x35LkSORb9YOMNkHPOtL78ada7uXzRlFtqq-FaQqy19SkeNoU~e-Z8wjqz79e8JXAJNBIJEANoqnHuMrXvyM.ST1un~P4rA3m.Acy7V23IBD5IAJLhLvrAt9iNYF08iUxpqzeMx.UQ5yEk.O8CnACwX8.-7MrVrhP.guhhUYexem9_wEHnDNF-zQNoyJo9x8GurSSbzMuc0M15EkXY.Qz4HRbTe9QfDKMNlFE65ZaairK5T0VL8QowSwIUCLI_rpD67Eyr7jSSx8DB56KnL38PdJ2qGDVnN3~MeR-0ItkrZVOexgDtK9uSOY2oRkArzddNg9EurRRNSWh3usJ5-VY_JAU~Fgp13TcSNWyHyOh35WOllXsIaqU_xnjTCApdKQhIML3byV3AkHFpGFaRG0L1.BXuL3~7rgEOsh9WmJeSYzZ4bLW3OmExUwcDKstZYWXkG4ZUKOp45pAE2ZNH.6WWvfRuKfeBwZBttgexpnETb4pATrcRpcY7mXrzLWOSoLRq7v1adFG5dwfWHqLeMt_NjvLbj8_RQaFyIj~PzH54ciDjf9ruY5zgno8tenecC9RbvJM3F~hXjjT2cBKufonRSEPVG4sML4LVFkeJ~LMmaHRaeeahyInSfahiKNv1YTk2jwcSEV3XU4W1yVB0UWUEQzywavLL1Xffl~PLJshun~OdM~eCcyzFoomNwWqs_2.wpJSI~5hz~weYcUtfoUtXGFZY1UA4vZK7KEH_g13_xXJy.4FppAEAxWoq4tL0Rb_3kZLvkbpKKiOXZAKiYL-4uimA0wjNXrMFgFTUs6zzulm09J7LycVzjmDCRigWayhQR38jXNjbg2qL8RjB.LwJSWQbPbJs6df.WZ6tH8yIXgv8ijSwUx/lantern-net-installer_windows.exe
2014-05-15 14:33:46,462 INFO     Uploading landing to 2Dh.rjQ7RMdSLopdoVbTK_qF2MHcvobbAVR0nBRohNyk2oUtSJxmdpo5fI8c6hlZ~mLkt1Ne8lN_x35LkSORb9YOMNkHPOtL78ada7uXzRlFtqq-FaQqy19SkeNoU~e-Z8wjqz79e8JXAJNBIJEANoqnHuMrXvyM.ST1un~P4rA3m.Acy7V23IBD5IAJLhLvrAt9iNYF08iUxpqzeMx.UQ5yEk.O8CnACwX8.-7MrVrhP.guhhUYexem9_wEHnDNF-zQNoyJo9x8GurSSbzMuc0M15EkXY.Qz4HRbTe9QfDKMNlFE65ZaairK5T0VL8QowSwIUCLI_rpD67Eyr7jSSx8DB56KnL38PdJ2qGDVnN3~MeR-0ItkrZVOexgDtK9uSOY2oRkArzddNg9EurRRNSWh3usJ5-VY_JAU~Fgp13TcSNWyHyOh35WOllXsIaqU_xnjTCApdKQhIML3byV3AkHFpGFaRG0L1.BXuL3~7rgEOsh9WmJeSYzZ4bLW3OmExUwcDKstZYWXkG4ZUKOp45pAE2ZNH.6WWvfRuKfeBwZBttgexpnETb4pATrcRpcY7mXrzLWOSoLRq7v1adFG5dwfWHqLeMt_NjvLbj8_RQaFyIj~PzH54ciDjf9ruY5zgno8tenecC9RbvJM3F~hXjjT2cBKufonRSEPVG4sML4LVFkeJ~LMmaHRaeeahyInSfahiKNv1YTk2jwcSEV3XU4W1yVB0UWUEQzywavLL1Xffl~PLJshun~OdM~eCcyzFoomNwWqs_2.wpJSI~5hz~weYcUtfoUtXGFZY1UA4vZK7KEH_g13_xXJy.4FppAEAxWoq4tL0Rb_3kZLvkbpKKiOXZAKiYL-4uimA0wjNXrMFgFTUs6zzulm09J7LycVzjmDCRigWayhQR38jXNjbg2qL8RjB.LwJSWQbPbJs6df.WZ6tH8yIXgv8ijSwUx/lantern-net-installer_windows.html
```