Update the build and bootstrap commands

[benogle]

The run command now has specs and is written in a reasonable way. The other two commands need to be updated to match.

Bootstrap command

• Upgrade to latest electron-rebuild
• Write specs
• Handle errors (see the run command as an example)
• Use the Utils.log methods (see the run command as an example)
• Use async/await rather than the async lib
• Pass all unused cli args through to the electron-rebuild binary

Build command

For all of these, see the run command as an example

• Make a decision on defaults for
  • --platform
  • --arch
  • --overwrite
• Write specs
• Handle errors
• Use the Utils.log methods
• Use async/await rather than the async lib
• Pass all unused cli args through to the electron-packager binary

cc @mnquintana