the plugins system for ltsp-build-client:

plugins are called by the "load_plugins" function. common plugins are located
in /usr/share/ltsp/plugins/ltsp-build-client/common, while vendor-specific
plugins are defined in /usr/share/ltsp/plugins/ltsp-build-client/VENDOR. if a
vendor plugin has the same filename as a common plugin, it will override the
common plugin. optionally, the admin can install or override common or vendor
plugins in /etc/ltsp/plugins/ltsp-build-client. 

NOTE:  Plugins are "sourced" not "executed", so be careful to avoid such things
as "exit" in your plugin scripts

there are several modes in which these plugins are called:

commandline:

builds the list of commandline arguments supported by the loaded plugins

configure:

sets variables for commandline options that are set

before-install:

before the initial chroot is built

install:

where the initial chroot is built (debootstrap, on debian systems)

after-install:

additional package installation(ltsp-client), tweaks, etc.

finalization:

the last steps needed, such as installing kernels, copying the kernels and
network bootable images into the tftp dir, installing the server's ssh keys
into the chroot, etc.
