Fixed `test-linkee` logic in `ProcessRemoteLinkTest::SetUp()`.
Fixed `test-linkee` logic in `ProcessRemoteLinkTest::SetUp()`.

Several problems existed on Windows here:

* The `BUILD_DIR` path has forward slashes (probably fine, but wrong).
* The executable must be named correctly, `.exe` and all.
* We should assert that `test-linkee` exists.
* The shell should not be used, otherwise `'(62)'` will resolve to an
  unknown UPID inside `test-linkee` because of the single quotes.

Review: https://reviews.apache.org/r/67977

kaysoky/mesos,jpeach/mesos,reneploetz/mesos,gsantovena/mesos,dforsyth/mesos,gsantovena/mesos,kaysoky/mesos,kaysoky/mesos,reneploetz/mesos,Gilbert88/mesos,Gilbert88/mesos,andschwa/mesos,Gilbert88/mesos,jpeach/mesos,abudnik/mesos,gsantovena/mesos,abudnik/mesos,dforsyth/mesos,dforsyth/mesos,dforsyth/mesos,andschwa/mesos,Gilbert88/mesos,chhsia0/mesos,abudnik/mesos,abudnik/mesos,abudnik/mesos,reneploetz/mesos,andschwa/mesos,Gilbert88/mesos,dforsyth/mesos,chhsia0/mesos,jpeach/mesos,Gilbert88/mesos,reneploetz/mesos,chhsia0/mesos,andschwa/mesos,jpeach/mesos,chhsia0/mesos,kaysoky/mesos,chhsia0/mesos,jpeach/mesos,abudnik/mesos,jpeach/mesos,kaysoky/mesos,gsantovena/mesos,dforsyth/mesos,jpeach/mesos,chhsia0/mesos,gsantovena/mesos,kaysoky/mesos,reneploetz/mesos,kaysoky/mesos,reneploetz/mesos,chhsia0/mesos,Gilbert88/mesos,andschwa/mesos,gsantovena/mesos,abudnik/mesos,dforsyth/mesos,andschwa/mesos,reneploetz/mesos,gsantovena/mesos,andschwa/mesos