Description of problem:
While creating a Search Bookmark using API, server does not require a 'public' attribute to be set, resulting new Bookmark entity with 'public': Null
- both foreman and katello entities are affected

Version-Release number of selected component (if applicable):

# rpm -q katello
katello-2.5.0-2.nightly.el7.noarch

# rpm -qa *katello
katello-2.5.0-2.nightly.el7.noarch
tfm-rubygem-hammer_cli_katello-0.0.19-1.el7.noarch
tfm-rubygem-katello-2.5.0-.201512150057git5d138841.nightly.el7.noarch
pulp-katello-0.4-3.el7.noarch



How reproducible:
always

Steps to Reproduce:
1. use POST request to create a bookmark for a random controller:

# curl -ku admin:changeme -H Content-Type:application/json -d "{\"name\": \"foo\", \"query\":\"bar\", \"controller\":\"architectures\"}" 'https://<FQDN>/api/bookmarks'

Actual results:
"public": null

{"name":"foo", "controller":"architectures","query":"bar","public":null,"id":1364,"owner_id":3,"owner_type":"User"}

Expected results:
"errors":{"public":["can't be blank"]}
or a default value true/false

Additional info: