Werk #7633: Add build support for Debian 9 (stretch)

Component	Linux distributions
Title	Add build support for Debian 9 (stretch)
Date	Feb 27, 2017
Level	Trivial Change
Class	New Feature
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	1.5.0i1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

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