package_manager: Use apt-ftparchive for deb packages

Use apt-ftparchive to create a Release file compatible with SecureApt.

apt-ftparchive is also a more efficient replacement of
dpkg-scanpackages:

root@neopili:~/curro/qtec/qt5022/build-qt5022-cesium/build/tmp/deploy/deb/bobcat
_64# time PSEUDO_UNLOAD=1 apt-ftparchive packages . >/tmp/kkk
real 0m26.873s
user 0m20.968s
sys 0m1.212s

root@neopili:~/curro/qtec/qt5022/build-qt5022-cesium/build/tmp/deploy/deb/bobcat
_64# time PSEUDO_UNLOAD=1 dpkg-scanpackages . >/tmp/kkk
dpkg-scanpackages: info: Wrote 6022 entries to output Packages file.
real 0m59.721s
user 0m16.668s
sys 0m11.164s

apt-ftparchive is not compatible with libpseudo. The calls to ftw()
returns the path in absolute format instead of relative. This
produces
wrong Packages and Release files.

ie:
MD5Sum:
d20227a958f6870137ce0e41b7b84307             1453
/home/ricardo/curro/qtec/qt5022/build-qt5022-cesium/build/tmp/deploy/deb/all/Release

This is why it is called with PSEUDO_UNLOAD.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>