Allow running the pimkolab tests.

Summary:
kdepim-runtime depends on ECM > 5.38, so the executable are created in
 the 'CMAKE_BINARY_DIR/bin' directory and not CMAKE_CURRENT_BINARY_DIR.

Note that this fix will cause more tests failures in kdepim-runtime.

Test Plan:
Before:
# ctest -R debugstreamtest
Test project /data/kde/build/kdepim-runtime
    Start 25: debugstreamtest
Could not find executable /data/kde/build/kdepim-runtime/resources/kolab/pimkolab/autotests/debugstreamtest

After:
# ctest -R debugstreamtest
Test project /data/kde/build/kdepim-runtime
    Start 25: debugstreamtest
1/1 Test #25: debugstreamtest ..................   Passed    0.18 sec

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D19981