Allow arbitrary build repo locations within the server's "sw" group

In order to be able to have build repositories stored in arbitrary locations within the server's base group sw, let's also use this groups path to find the repos. This allows to use for example

init-env -u customer/build-customer

to be used to initialize the repo build-customer located in the subgroup customer within the group sw. The other search locations like the yocto-customer group are kept for compatibility.

We also make sure that the build-repo is cloned to the root directory (yocto-ktn) locally and the remote group hierarchy is discarded.

See ked-intern/ked-docu#801 for more background information.