use g_path_get_basename instead of basename

use g_path_get_basename instead of basename

basename(3) and dirname(3) modify their argument and may return
pointers to statically allocated memory which may be overwritten by
subsequent calls.
g_path_get_basename and g_path_get_dirname have no such issues, and
therefore more preferable.

Signed-off-by: Julia Suvorova <[email protected]>
Message-Id: <1519888086[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>