Fix for the UI boundary tests.

Boundary tests need a fixed length to test whether the entity
creation beyond 255 chars fails. It is here where we do require
an option to specify a fixed length.

so now unless we specify a length for the string it will continue
to use a random length for non-boundary tests.

Added sphinx directives
Merge pull request #1476 from kbidarkar/fix-UI-boundary-tests

Fix for the UI boundary tests.
(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.