makechrootpkg: Don't mount-bind srcdest/pkgdest

Do actual copying to and from PKGDEST and SRCDEST rather than
mounting via --bind, as the chown and other operations can cause
issues here

Original-work-by: Phil Dillon-Thiselton <dibblethewrecker@gmail.com>
Signed-off-by: Aaron Griffin <aaronmgriffin@gmail.com>