Improve seeder(v1) to send big values

[adiholden]

Cluster tests use DflySeederFactory which does not send big value by default
We should change this to send few big entries in order to test big values in all cluster test

[chakaz]

I only briefly looked into this issue, my very initial changes are in the branch chakaz/seeder-huge
This change is not enough because we create huge commands there, which are too long for a single command and dragonfly rejects it. It's not the command itself that's too long, but the number of arguments.
We can modify the seeder to use bigger chunks with smaller arguments for the huge values. But it's yet to be proven that our tests will pass with that change..