Update gtest from 1.9 to 1.10

[calgray]

Optional cuda support in unit tests can be improved using the new feature GTEST_SKIP in 1.10

#else
    GTEST_SKIP_("Library built without CUDA support, skipping CUDA test");
#endif

The the rest of the ifdefs in the test file will then be unnecessary and don't need to manually skip/disable tests.
Of course if you change to a runtime check then this would be slightly different, but the same idea.