Improve again the release script
Improve again the release script

The script now accepts one optional parameter (--changelog/-c) that will
generate the changelog, ordered by commit time.
Only the first line of the commit message will be printed.

Change-Id: Id1af42148f2d24090ee126577518432c83778a7e

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server