Add secops guides for network and hosts

[karenzone]

Continuation from #189

[nik9000]

The PR tests here found something but they didn't log things very well......

[karenzone]

@elastic/secops I've updated the docs framework to give you two books (network and hosts) based on comments from @andrewkroh in #189. Picturing a new book based on asciidoc files can be tough, so

DeDe wrote our first solution guide for Infrastructure (https://www.elastic.co/guide/en/infrastructure/guide/current/index.html). Her guide has a nice user-centered flow to it, and I've followed her info architecture in these new security guides.

We'll also need to add some info similar to this to the Kibana Reference.

[tsg]

@karenzone I've noticed a .DS_store file in the PR, you should remove that.

[andrewkroh]

The structure seems good. Not sure what's causing the test failure.

[nik9000]

Since this test is a new one from me I'll see what I can find locally.

[nik9000]

OK! The tests are failing because your PR is quite out of date with master and it is missing some files that it needs to run the tests, specifically it is missing the "installation and upgrade guide". Merging mater into this branch ought to fix it. I'll improve the error message in the mean time.

[nik9000]

That merge did the trick!