Fix return code for BLAS complex api check

[ndellingwood]

Follow-on to PR #374

[kyungjoo-kim]

Thanks.

[ndellingwood]

@kyungjoo-kim here is the CMake BLAS check update we worked on. Previously failing gs tests on White with Trilinos with complex and gcc/7.2 compiler are now passing (see this comment link for cdash report)

[ndellingwood]

Can also confirm all complex<double> tests are passing with gcc/7.2 in Trilinos:

Test project /ascldap/users/ndellin/trilinos/Trilinos/Build/Issue-2426-override/kokkos-kernels/unit_test
    Start 1: KokkosKernels_blas_openmp_MPI_1

1/8 Test #1: KokkosKernels_blas_openmp_MPI_1 .....   Passed  537.19 sec
    Start 2: KokkosKernels_sparse_openmp_MPI_1
2/8 Test #2: KokkosKernels_sparse_openmp_MPI_1 ...   Passed   41.33 sec
    Start 3: KokkosKernels_graph_openmp_MPI_1
3/8 Test #3: KokkosKernels_graph_openmp_MPI_1 ....   Passed   10.86 sec
    Start 4: KokkosKernels_common_openmp_MPI_1
4/8 Test #4: KokkosKernels_common_openmp_MPI_1 ...   Passed    0.37 sec
    Start 5: KokkosKernels_blas_serial_MPI_1
5/8 Test #5: KokkosKernels_blas_serial_MPI_1 .....   Passed  807.77 sec
    Start 6: KokkosKernels_sparse_serial_MPI_1
6/8 Test #6: KokkosKernels_sparse_serial_MPI_1 ...   Passed   57.46 sec
    Start 7: KokkosKernels_graph_serial_MPI_1
7/8 Test #7: KokkosKernels_graph_serial_MPI_1 ....   Passed   18.35 sec
    Start 8: KokkosKernels_common_serial_MPI_1
8/8 Test #8: KokkosKernels_common_serial_MPI_1 ...   Passed    0.45 sec

[mhoemmen]

Awesome! :D

@micahahoward @rrdrake @theguruat12