Improve SCM wrapping

[imphil]

The SCM provides a system reset functionality which we didn't explicitly expose in osd_cl_scm so far. Add that.

Also wrap this functionality in the Python API.

[koenenwmn]

When I try to import osd after installing this version I get an ImportError: <path_to_osd-sw>/src/python/osd.cpython-35m-x86_64-linux-gnu.so: undefined symbol: osd_cl_scm_system_reset
Same problem when I run the tests:

______________________________________________________________________________________________________________________ ERROR collecting tests/test_core.py _______________________________________________________________________________________________________________________
ImportError while importing test module '<path_to_osd-sw>/src/python/tests/test_core.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_core.py:16: in <module>
    import osd
E   ImportError: <path_to_osd-sw>/src/python/osd.cpython-35m-x86_64-linux-gnu.so: undefined symbol: osd_cl_scm_system_reset
_____________________________________________________________________________________________________________________ ERROR collecting tests/test_hostmod.py _____________________________________________________________________________________________________________________
ImportError while importing test module '<path_to_osd-sw>/src/python/tests/test_hostmod.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_hostmod.py:20: in <module>
    import osd
E   ImportError: <path_to_osd-sw>/src/python/osd.cpython-35m-x86_64-linux-gnu.so: undefined symbol: osd_cl_scm_system_reset

[imphil]

You need to rebuild and install libosd first to make this symbol available.

(libosd as from this branch.)