tests: Link some mocks with libtest_qemu_driver.so

tests: Link some mocks with libtest_qemu_driver.so

I've noticed some tests fail to run under valgrind with the
following error:

  $ valgrind --leak-check=full --trace-children=yes ./qemuxmlconftest
  valgrind: symbol lookup error: libvirt.git/_build/tests/libdomaincapsmock.so: undefined symbol: virQEMUCapsGet

But without valgrind the test passes just fine. While we usually
don't want to change our code just to adhere to random tools, in
this case we ought to make an exception because valgrind helps us
to detect memory leaks.

NB, the --trace-children=yes is needed whenever a test
re-executes itself, i.e. when it uses mocks. Otherwise we'd just
get (boring) result for the first invocation of main() which does
nothing more than sets up the environment and calls exec().

When running the test binary without valgrind I can see the
libtest_qemu_driver.so being loaded even after exec:

$ LD_DEBUG=libs ./qemuxmlconftest 2>&1 | grep -e libtest_qemu_driver.so -e virQEMUCapsGet
      6439:     find library=libtest_qemu_driver.so [0]; searching
      6439:       trying file=libvirt.git/_build/tests/../src/libtest_qemu_driver.so
      6439:       trying file=libvirt.git/_build/tests/glibc-hwcaps/x86-64-v3/libtest_qemu_driver.so
      6439:       trying file=libvirt.git/_build/tests/glibc-hwcaps/x86-64-v2/libtest_qemu_driver.so
      6439:       trying file=libvirt.git/_build/tests/libtest_qemu_driver.so
      6439:     calling init: libvirt.git/_build/tests/libtest_qemu_driver.so
      6439:     find library=libtest_qemu_driver.so [0]; searching
      6439:       trying file=libvirt.git/_build/tests/libtest_qemu_driver.so
      6439:     calling init: libvirt.git/_build/tests/libtest_qemu_driver.so
      6439:     calling fini: libvirt.git/_build/tests/libtest_qemu_driver.so [0]

But running the same under valgrind:

$ LD_DEBUG=libs valgrind --leak-check=full --trace-children=yes ./qemuxmlconftest 2>&1 | grep -e libtest_qemu_driver.so -e virQEMUCapsGet
      6515:     find library=libtest_qemu_driver.so [0]; searching
      6515:       trying file=libvirt.git/_build/tests/../src/libtest_qemu_driver.so
      6515:       trying file=libvirt.git/_build/tests/glibc-hwcaps/x86-64-v3/libtest_qemu_driver.so
      6515:       trying file=libvirt.git/_build/tests/glibc-hwcaps/x86-64-v2/libtest_qemu_driver.so
      6515:       trying file=libvirt.git/_build/tests/libtest_qemu_driver.so
      6515:     calling init: libvirt.git/_build/tests/libtest_qemu_driver.so
      6515:     libvirt.git/_build/tests/libdomaincapsmock.so: error: symbol lookup error: undefined symbol: virQEMUCapsGet (fatal)
valgrind: symbol lookup error: libvirt.git/_build/tests/libdomaincapsmock.so: undefined symbol: virQEMUCapsGet

To me, it looks like valgrind forced linker to lookup symbols
"sooner", as individual libraries are loaded. But I must admit I
have no idea how valgrind does that (or if that's even valgrind's
'fault').

But fix is pretty simple: link mocks that rely on symbols from
the QEMU driver with the QEMU driver, well, its test suite
suitable version (libtest_qemu_driver.so).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>