Enable mysql/pg tests in travis.
Merge branch 'stable'

* Rewrite box_net.{pg,mysql}.test.lua, so line wrappings won't matter.
* Testing System: 'RelWithDebugInfo' closer to Release, than to Debug
* Compiling on clang -> additional OP, cause of garbage after
  `iproto_request_type_strs` (Failed admin and other tests)