#148: Belos: Update all `*_diag.cpp` tests to use `Tpetra`

[cwschilly]

Fixes #148

• [x] test_bl_gmres_multidiag.cpp
• [x] test_bicgstab_diag.cpp
• [x] test_bl_gmres_diag.cpp
• [x] test_minres_diag.cpp (#70)
• [x] test_tfqmr_diag.cpp (#135)

[cwschilly]

A few points regarding test_bl_gmres_multidiag.cpp:

1. While the name of the file and comments suggest it uses the block GMRES to solve, the actual implementation (in the original Epetra version) used the pseudo-block GMRES solver. This is what I used in the Tpetra version. Should I change the name of the file(s) to reflect this (eg test_pseudo_gmres_multidiag.cpp)?
2. There was no existing MultiMatrixSolve folder in the tpetra directory, so I put this test in the existing MultipleSolves directory.
3. I created a duplicate "BelosLinearMultiShiftProblem.hpp" (currently in epetra/test/MultiMatrixSolve) and placed it in the MultipleSolves directory (tpetra/test/MultiplesSolves)

[cwschilly]

@stmcgovern This PR is ready for review. It adds three of the five *_diag.cpp tests (with the other two being handled in separate PRs, as noted in the initial comment).