Tests fail on RHEL-6 because libmytap.so is not found

running `make test` fails with errors like:

  1/ 55 Testing pcre_test                        Passed

  2/ 55 Testing pcre_grep_test                   Passed

  3/ 55 Testing strings                       ***Failed 

  4/ 55 Testing simple                        ***Failed 

  5/ 55 Testing skip                          ***Failed 

and so on.

running `/usr/bin/ctest --force-new-ctest-process --verbose` showed me errors like:

/builddir/build/BUILD/mariadb-10.0.15/unittest/strings/strings-t: error while loading shared libraries: libmytap.so: cannot open shared object file: No such file or directory

After analysing build log I see difference between RHEL-6 and Fedora such as there is the following rpath definition more on Fedora when building strings-t binary (one of the unittests):

-Wl,-rpath,/builddir/build/BUILD/mariadb-10.0.15/unittest/mytap

and that is also reason why tests pass on Fedora.

My workaround for allowing the test binaries to find mytap library also works:

LD_LIBRARY_PATH=$(pwd)/unittest/mytap make test

RHEL-6 includes cmake-2.6.4 and Fedora 21 includes cmake-3.0.2, but since it works fine in 5.5.x I guess it should be possible to fix it in CMake configs somehow. But my knowledge of CMake is not good enough to provide a patch.