Teach rails the singular of Quota

This is required for reporting purposes where we actively "singularize" the name
of model objects in order to contantize and load them.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Add Cloud Tenants and ResourceQuotas to reports

Allow users to select fields from CloudTenants and CloudResourceQuotas in
reports.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Add more models to reports

* Flavors
* Availability Zones
* Security Groups

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Add MiqExpression.determine_relat_path

to build the model relationship path correctly if class_name is specified for an association.
The :parent,:path field built in the model relationship tree is used to populate the Available Fields in reporting.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Add test cases for MiqExpression.determine_relat_path and .build_relats.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Use EmsCloud for the association to ext_management_system for the cloud models.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Add EmsCloud and EmsInfra to report base tables.

So reports can be created based on these two models.
https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Workaround to exclude infra models from EmsCloud relationships.

These infra models are inherited from ExtManagmentSystem class.

https://bugzilla.redhat.com/show_bug.cgi?id=1133132
Merge pull request #585 from blomquisg/bz1133132-no-tenant-fields-in-reporting

Bz1133132 add new cloud models to reporting