Use Clean-Session from Connection Options

[DerTim1]

The Option clean_session is already implemented, but always set to true.

This PR adds 2 lines to be able to set clean_session as false with connection_options.

Unfortunately I can't run tests with Elixir 1.10, because the QuickCheck library can't be downloaded (is fixed in eqc, but not released yet, see https://github.com/Quviq/eqc_ex/commit/1e8367293a06de050bbceffc53ac2aca7696dae7) and a further problem in eqc_ex.

[coveralls]

Pull Request Test Coverage Report for Build 4

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.671%

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Totals
Change from base Build 57:	0.0%
Covered Lines:	576
Relevant Lines:	657

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💛 - Coveralls

[DerTim1]

Ping... This is trivial fix. Can we merge that?