The install_pxe_bootloader_to_run_dir procedure is required by the tftp
as well as the ipxe load script. Move it to a separate file which is
include by both.
'unzip' can uncompress and load raw multiboot images and ELF files.
Usage together with the PXE bootloader ease life running the muen hypervisor
together with a Genode/x86_64 VM, where the raw boot image is typically quite
large.
Ref #2358
If a user has e.g. /tftpboot/x86 as directory and configures
base_dir=/tftboot and offset_dir=/x86, this leads to bad behavior
as the load module creates a symlink
/tftpboot/x86/<builddir> -> <absolut_builddir>
in this case instead of the desired
/tftpboot/x86 -> <absolut_builddir>
Furthermore, the module works on
/tftpboot/x86/config-00-00-00-00-00-00
and
/tftpboot/x86/<builddir>/config-00-00-00-00-00-00
afterwards, which looks bad too. As there is no warning at all, this can
be hard to debug. The commit adds an appropriate check with error message and
exit -1 on an existing directory.
Fixes#1630
