Add a script to build REC images

This can be executed locally as well as in Jenkins to create REC images.

To create REC image also manifest RPM must be built to get build
information included to the REC runtime environment. This information
can be then used within the REC to indentify which build has been
installed.

The "rpmbuilder" tool (that uses "mock") is way too heavy for manifest
RPM creation thus Alpine based build environment was chosen. Manifest
RPM has no dependencies thus this should be ok although experimental.

Change-Id: Ic2ca3115bbfbbac89bf3139c47f8467a76ebd0b6
Signed-off-by: Saku Chydenius <saku.chydenius@nokia.com>