package/opkg: disable tests and manpages

Changeset f1d3e098 (Build shared libraries only as the default) broke the
opkg package.

opkg wants to link its testsuite statically with the internal libopkg.
But in a shared-only build, there is no static library.

Since for Buildroot we do not care about tests, just disable them.

Fixes numerous build failures;
    http://autobuild.buildroot.net/results/ddf/ddf4b38c1df73b00b76be71db3f1eb8b1d932c55/
    http://autobuild.buildroot.net/results/c1c/c1c9a21b6583c9ef3ddd32681bb13cf91a218e8c/
    http://autobuild.buildroot.net/results/284/284bf7d6f9cebf8633143ca1ce15154de941805f/


    ...

Disable manpages at the same time.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Peter Korsgaard <jacmet@uclibc.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>