smis.py: Handle _enumerate property list better
smis.py: Handle _enumerate property list better

For some providers they don't handle None being passed in for
PropertyList so we will only include it when it has a value.

Signed-off-by: Tony Asleson <1ef2d381aa56d512126ddaacc29e68136e4fdf55@redhat.com>

jumitche/libstoragemgmt,lazy404/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,tasleson/libstoragemgmt,joehandzik/libstoragemgmt,joehandzik/libstoragemgmt,tasleson/libstoragemgmt,libstorage/libstoragemgmt,lazy404/libstoragemgmt,cathay4t/libstoragemgmt,libstorage/libstoragemgmt,joehandzik/libstoragemgmt,libstorage/libstoragemgmt,jumitche/libstoragemgmt,joehandzik/libstoragemgmt,libstorage/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,cathay4t/libstoragemgmt,cathay4t/libstoragemgmt,tasleson/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,lazy404/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt,lazy404/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,libstorage/libstoragemgmt,cathay4t/libstoragemgmt