opkg: fix installation of dev / dbg packages

opkg: fix installation of dev / dbg packages

OE-Core revision ffe93e2a099e4cadb1829dc12a58a6d7bef9a5a7 moved opkg's
configuration file into /etc/opkg, and opkg always reads all files under
this directory even if -f is specified (as it is during do_rootfs in
order to specify our own generated config file), and this means that
after opkg-collateral is installed into the rootfs, this version of the
config is used, resulting in opkg ignoring the list of packages it has
already downloaded (since it now sees list_dir as /var/lib/opkg instead
of the default /var/lib/opkg/lists) and thus it fails to install any of
the "attemptonly" packages (including *-dev, *-dbg, etc.).

If we change the -f option to ignore configuration files in /etc/opkg
then we no longer have this problem.

Fixes [YOCTO #2595].

(From OE-Core rev: 37df134557802ba116f001597b7cd5e9bc39e188)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>