Default verbosity for building packages

We now default to verbose output when building, testing, and installing
the packages specified on the command line for the corresponding `buzzy`
commands.  We still default to non-verbose output for any prereqs that
we decide to install ourselves.
Create package destination directory

Otherwise we get an error when trying to build the package.
Print non-verbose output when error occurs

Before, in non-verbose mode, our helper function for running a command
would just drop the stdout and stderr output.  We now collect it into a
buffer, so that if there's an error running the command, we can tell the
user why.