Don't hardcode chroot executable path
Remove unused modules
fixes case where name is omitted from pip arg list

This code:
```
    if name.endswith('.tar.gz') or name.endswith('.tar.bz2') or
name.endswith('.zip'):
        is_tar = True
```
was not checking whether name is defined since it is an
optional param.
Override destination file name/path, supports relative paths too.