Introduced ABORT as alternative to fatal.

Review: https://reviews.apache.org/r/18549
Removed define for gtests to use its own tr1 tuple.

gtest's tr1::tuple conficts with std::tr1::tuple for gcc-4.4. However,
we use tuple throughout mesos so we assume tr1::tuple or tuple is
available. As such, we don't need gtest to define one.

Review: https://reviews.apache.org/r/18722
Introduced CHECK_* for Future and use of ABORT.

Review: https://reviews.apache.org/r/18550
Added TaskID validation check.

Review: https://reviews.apache.org/r/18339
Added a flag to review bot to specify number of reviews to verify.

Review: https://reviews.apache.org/r/18827