This is like building the root image but using a specific strongSwan
source tree, which is helpful if code changes depend on other software
packages (e.g. TKM-related or testing new crypto libraries). If the script
is called and the root image does not exist, the new option is enabled
automatically.
The option to build in a specific guest image is now also moved to an
explicit command line option so that the source dir path is the only
remaining positional argument (see --help for details).
This allows to (relatively) quickly (re-)build and install the current
or an arbitrary strongSwan source tree within the root image.
bindfs is used to bind mount the source directory using the regular user
and group (only works if sudo is used to run the script) so that newly
created files are not owned by root.
As with building the root image in general the guests must not be
running while executing this script. The guest images are automatically
rebuilt after the root image has been updated so configuration files and
other modifications in guests will be lost.