[WIP] Implement "hit build --copy xx"

The `--copy` functionality was implemented in old hashstack in the commit https://github.com/hashdist/hashstack/commit/b86979979cf894f80ac064e5a598499580b8291f. Most of the functionality from hashstack has now been ported to hashdist, so I have ported that patch over in this PR.

Unfortunately, the essential `make_profile` function used to be defined in 
[hashdist/core/profile.py](https://github.com/hashdist/hashdist/blob/00f1d85c8de29035be066bc004956d8b867a87b9/hashdist/core/profile.py), which was removed in 56a3dfb01475bd374bbe30779b76c5d0a92ee1f3, so the current PR fails with:
```
ondrej@kittiwake:~/repos/hashstack2(master)$ hit build --copy xx
[ERROR] Uncaught exception:
Traceback (most recent call last):
  File "/auto/nest/nest/u/ondrej/repos/hashdist/hashdist/cli/main.py", line 168, in help_on_exceptions
    return func(*args, **kw)
  File "/auto/nest/nest/u/ondrej/repos/hashdist/hashdist/cli/main.py", line 142, in main
    retcode = args.subcommand_handler(ctx, args)
  File "/auto/nest/nest/u/ondrej/repos/hashdist/hashdist/cli/frontend_cli.py", line 32, in run
    self.profile_builder_action()
  File "/auto/nest/nest/u/ondrej/repos/hashdist/hashdist/cli/frontend_cli.py", line 56, in profile_builder_action
    from ..core import atomic_symlink, make_profile
ImportError: cannot import name make_profile

This exception has not been translated to a human-friendly error message,
please file an issue at https://github.com/hashdist/hashdist/issues pasting
this stack trace.
```

@dagss --- how do I port this PR to the new hashdist? Why was `profile.py` removed?