ETCH-292 Enable build for several platforms in a row

In order to be able to build several platforms in a row the build
artifacts must be stored in separate folders. Therefore the build folder
now containes the platform specifications like operating system and
architecture.

Change-Id: I75ce8e174b4944ed72324bce0497ee7f7d50a4b1

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1579900 13f79535-47bb-0310-9956-ffa450edef68