gen_update: add conf and cmd functionality

a conf_dir and cmd_dir can be specified as parameters. If given, the files
included in this directories are added to the update package. If given, a
XML file will be optional and no debian packages may be included in the update
file.

Signed-off-by: Manuel Traut <manut@linutronix.de>
genupdatepkg: always include a version of new.xml

updated uses it to determine the destination of update archive extraction

Signed-off-by: Manuel Traut <manut@linutronix.de>
updated: use cmd and conf diretories

if one of the above mentioned directory exist, cp the files to the rfs (conf)
  or try to execute all files in the directory (cmd).

For copying the conf files, the according filesystems are remounted
read-writeable (if mounted read-only).

The scripts in cmd need to bother about remounting by their own, because i
can't know what they like to touch.

Signed-off-by: Manuel Traut <manut@linutronix.de>
postbuild: add a hook for a postbuild script

this hook is called after a project build

this patch also changes the storage format of elbeproject.presh_file and
elbeproject.postsh_file from open filehandle to string pointing to the
file on the drive
updated: use os.system instead of execute for apt-get clean

Signed-off-by: Manuel Traut <manut@linutronix.de>
updated/cp conf files: catch IOError

thrown if sth. should be copied to a read-only media, eg. cdrom

Signed-off-by: Manuel Traut <manut@linutronix.de>
db: add timestamp to ProjectVersion

Signed-off-by: Manuel Traut <manut@linutronix.de>
init-vm: forward host hw random generator into vm

Signed-off-by: Manuel Traut <manut@linutronix.de>

Conflicts:
	elbepack/init/preseed.cfg.mako