Description of problem:
If installed into system without python-copr package installed, it fails with traceback.

Version-Release number of selected component (if applicable):
0.8.0-2.fc24, 0.8.0-2.fc26

How reproducible:
Always

Steps to Reproduce:
1. dnf install rebase-helper
2. rebase-helper

Actual results:
Traceback (most recent call last):
  File "/usr/bin/rebase-helper", line 9, in <module>
    load_entry_point('rebasehelper==0.8.0', 'console_scripts', 'rebase-helper')()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 547, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2720, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2380, in load
    return self.resolve()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2386, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python2.7/site-packages/rebasehelper/cli.py", line 30, in <module>
    from rebasehelper.application import Application
  File "/usr/lib/python2.7/site-packages/rebasehelper/application.py", line 30, in <module>
    from rebasehelper.specfile import SpecFile, get_rebase_name
  File "/usr/lib/python2.7/site-packages/rebasehelper/specfile.py", line 33, in <module>
    from rebasehelper.utils import DownloadHelper, DownloadError, MacroHelper, defenc
  File "/usr/lib/python2.7/site-packages/rebasehelper/utils.py", line 37, in <module>
    import copr
ImportError: No module named copr


Expected results:
usage: rebase-helper [-h] [-v] [-p] [-b] [--buildtool BUILDTOOL]
                     [--pkgcomparetool PKGCOMPARETOOL]
                     [--outputtool OUTPUTTOOL] [-w] [--not-download-sources]
                     [-c] [--non-interactive] [--comparepkgs-only COMPAREPKGS]
                     [--builds-nowait] [--build-tasks BUILD_TASKS]
                     [--results-dir RESULTS_DIR]
                     [--build-retries BUILD_RETRIES]
                     [--builder-options BUILDER_OPTIONS]
                     SOURCES

too few arguments

Package does depend on python-copr and is installed with it, or it does not require it unless I am building copr package.

Additional info:
rebase-helper --build-tool=mock
does not help.