hack: allow tested code to know it is being tested (bnc#893965)

export Y2ALLGLOBAL like yast2-testsuite does it
The tested code is ag_netd in yast2.rpm.

In fact the tests should live there, but then the tests would not work
because of a bug in path search that is risky to fix now.
See https://github.com/yast/yast-core/pull/82/