Add support for building debian package

Files necessary for building .deb package.  This is very early version. Know bugs from lintian:
E: cf-keycrypt: binary-or-shlib-defines-rpath usr/sbin/cf-keycrypt /var/cfengine/lib
W: cf-keycrypt: hardening-no-relro usr/sbin/cf-keycrypt
E: cf-keycrypt: possible-gpl-code-linked-with-openssl