use libarchive directly

[pohly]

This is related to clearlinux/swupd-server#48. Once the server uses libarchive, the client should also use bsdtar, which is already possible.

But calling libarchive directly would have several advantages:

• when unpacking Manifest files, restoring file attributes can be skipped, thus avoiding a problem with "ioctl(4, FS_IOC_GETFLAGS, 0x7ffe5c46d874) = -1 ENOTTY (Inappropriate ioctl for device)" when the statedir is on a tmpfs
• tar archives can be unpacked directly, without storing the entire file on disk first (GNUtar needs to seek in the file to detect compression methods, libarchive doesn't)
• file name or link name encoding errors in a locale which does not support UTF-8 can be ignored because the fallback is to skip re-encoding, which is exactly what swupd needs (would solve bsdtar: ignore UTF-8 encoding errors #280)

Right now, #249 is implemented with statedir on the target partition (because of #273), but then the target partition must have at least enough space for "unpacked rootfs + pack-os-core-from-0.tar".

[pohly]

The goal is to do "swupd verify --install -p /mnt/some-partition" and directly stream the OS content onto the target partition (needed for issue #249).

Right now we put the state directory onto the target partition (partly because of issue #273, partly because unpacking Manifests into /tmp fails due to the ioctl() problem), but that means that additional space is needed on the OS partition.

[matthewrsj]

Fixed by #327