libroot: Style fix
libroot: Pass members to filter as on-target variable
Allow stripping binaries when copying to image containers

Currently only needed for boot floppy on some platforms.

Disabled for now.

Note we do not have a mean of knowing which file is a binary
or not so we just try to strip, and silently continue when
strip fails (like on the kernel settings file).

Also note strip actually replaces the file, which means it looses
both the resources and attributes, which shouldn't be a problem
for the boot floppy drivers archive, but is not wanted for other
images, so it's not usable elsewhere as such. Patch wanted.