elbeproject: use get functions to retrieve rpcaptcache

always use the get function to retrieve the rpcaptcache to ensure
that an instance exists.

Signed-off-by: Manuel Traut <manut@linutronix.de>
buildchroot: add option to skip pkglist section

this can be used to speedup image generation for testing modifications
in the archive or finetuning section.

changes of the pkg-list will be ignored if elbe buildchroot is called
with the --skip-pgklist parameter.

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

this patch allows the definition of btrfs filesystems.

Signed-off-by: Manuel Traut <manut@linutronix.de>
finetuning: ln - add missing braces

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