generate sparse file

The previous version of the dd command filled the files with 0.
The new version creates a sparse file (still read as 0) reducing
disk usage on supported file systems.
get_exec_libs: avoid unnecessary copy
get_exec_lib: parse for libs recursively
buildquagga: get library dependencies of installed libraries as well
fetch_lib: hack to make it work on some 64 bit systems

not generic enough!
splitting buildguest in two

Buildguest was installing the guest image as well, which
made additions to the guest image cumbersome. Now build
and install are separated.
adding buildquagga to the monolithic build