Added signature write to .sig file

Added signature write to .sig file

To enable module signature verification working on file systems
without extended attributes, or to be able to copy modules by methods,
which does not support extended attribute copying, it is necessary
to store signature in the file. This patch provides command line parameter
for storing signature in .sig file.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>