Explicitly state that this marks the `.xml` to tell the dashboard
server to append it to previously submitted results and that it
does not cause results to be appended to the `.xml` file.
If a `ctest_*` command has CAPTURE_CMAKE_ERROR then any errors generated
by cmake during that command will cause the value to be assigned `-1`.
This will prevent a `ctest -S` script from returning non-zero unless the
script explicitly calls `message(FATAL_ERROR)`.
Brad King
Bill Hoffman
Zack Galbreath
Kitware Robot