futures_test: Test using future::then with functions
futures_test: Test using future::then with functions

This was unintentinally fixed by 0ecf8222a003774cb641d16cd9c714feb1d71a19.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>
Message-Id: <20200622170755.171578-1-1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

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