Description of problem:
There are many places, where user is forced to set an attribute when there is only one option available.
e.g. New Host -> Location.
If there's only 'Default Location, the field remains 'null' by default and user is forced to manually set it before he's able to proceed with creating new host.It is simply annoying, we could provide better user experience if the fields with one option are auto-populated.

Similar thing happens on OS and provisioning templates. If a new kind of provisioning template is assigned to OS (e.g. PXEGrub template), a 'PXEGrub template' field will appear under OS->Provisioning templates.
Despite the fact, that only a single template has been assigned to the OS, the field is not being set and remains 'Null', causing an error during the actual provisioning.

How reproducible:
always

Steps to Reproduce:
1. have a single org and loc (e.g. default ones)
2. Navigate to Hosts -> New Hosts
3. notice the Organization & Location fields are marked as mandatory and are set to 'null' by default despite the fact, there is only 1 possible option for them - Forcing user to set it manually.

Actual results:
the mandatory fields with 1 possible value are not set, causing the values for the rest of the form not being filtered by the taxonomies, allowing user to choose invalid values before he sets the taxonomies themselves.

Expected results:
Set the values automatically everywhere, where possible.

Additional info:
The New Host dialog is not the only place, where similar thing happens.