Add configuration options for host/port

Prior to this commit, the import/export tools had hard-coded
values of "localhost" and 8080 for the PuppetDB host/port.
This commit simply adds configuration options that allow you
to override the defaults.
WIP: export now writes directly to a tarball

Need to add tests for tarball code, which will probably be easier
after I've implemented the read functionality.

Need to port `import` command over to do the same.