(API) Port old tests for hosts

Significantly update the definition of class `Host`: modify fields and override
the `build` method to properly create dependent entities. Enable CRUD tests for
hosts in module `test_multiple_paths`. Drop old CRUD tests for hosts.

Slightly clean up module `test_host_v2`.

Fix #1446.
I've sorted all fields alphabetically and altered a few of their definitions too. For example, some fields weren't properly marked as required.