I just tried with logstash 5.2.1 and I was able to set http.host: 192.168.0.187 which is my local lan ip.
can you make sure your logstash.yml line isn't commented out?
Are there any error messages? Also, if you run logstash with --log.level=debug it will print all settings at the start, and say which ones are modified:
/tmp/logstash-5.2.1 % bin/logstash -e "" --log.level=debug
[2017-04-07T11:53:37,932][DEBUG][logstash.runner ] -------- Logstash Settings (* means modified) ---------
[2017-04-07T11:53:37,935][DEBUG][logstash.runner ] path.data: "/tmp/logstash-5.2.1/data"
[2017-04-07T11:53:37,935][DEBUG][logstash.runner ] *config.string: ""
[2017-04-07T11:53:37,935][DEBUG][logstash.runner ] config.test_and_exit: false
[2017-04-07T11:53:37,935][DEBUG][logstash.runner ] config.reload.automatic: false
[2017-04-07T11:53:37,935][DEBUG][logstash.runner ] config.reload.interval: 3
[2017-04-07T11:53:37,936][DEBUG][logstash.runner ] metric.collect: true
[2017-04-07T11:53:37,936][DEBUG][logstash.runner ] pipeline.id: "main"
[2017-04-07T11:53:37,936][DEBUG][logstash.runner ] pipeline.workers: 4
[2017-04-07T11:53:37,937][DEBUG][logstash.runner ] pipeline.output.workers: 1
[2017-04-07T11:53:37,937][DEBUG][logstash.runner ] pipeline.batch.size: 125
[2017-04-07T11:53:37,937][DEBUG][logstash.runner ] pipeline.batch.delay: 5
[2017-04-07T11:53:37,937][DEBUG][logstash.runner ] pipeline.unsafe_shutdown: false
[2017-04-07T11:53:37,937][DEBUG][logstash.runner ] path.plugins: []
[2017-04-07T11:53:37,938][DEBUG][logstash.runner ] config.debug: false
[2017-04-07T11:53:37,938][DEBUG][logstash.runner ] *log.level: "debug" (default: "info")
[2017-04-07T11:53:37,938][DEBUG][logstash.runner ] version: false
[2017-04-07T11:53:37,939][DEBUG][logstash.runner ] help: false
[2017-04-07T11:53:37,939][DEBUG][logstash.runner ] log.format: "plain"
[2017-04-07T11:53:37,939][DEBUG][logstash.runner ] *http.host: "192.168.0.187" (default: "127.0.0.1")