dracut-install: preserve extended attributes when copying files

dracut-install: preserve extended attributes when copying files

Preserve extended attributes when copying files using dracut-install.

The copying of extended attributes avoids file execution denials when
the Linux Integrity Measurement's Appraisal mode is active. In that mode
executables need their file signatures copied. In particular, this patch
solves the problem that dependent libaries are not included in the
initramfs since the copied programs could not be executed due to missing
signatures. The following audit record shows the type of failure that
is now prevented:

type=INTEGRITY_DATA msg=audit(1477409025.492:30065): pid=922 uid=0
 auid=4294967295 ses=4294967295
 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
 op="appraise_data" cause="IMA-signature-required"
 comm="ld-linux-x86-64"
 name="/var/tmp/dracut.R6ySa4/initramfs/usr/bin/journalctl"
 dev="dm-0" ino=37136 res=0

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>