throw more descriptive errors when collection .json is invalid

[rkirov]

For example https://github.com/angular/devkit/blob/master/packages/angular/schematics_tools/src/file-system-engine-host.ts#L60 just returns null, which means the error thrown eventually is the same as the file is missing and etc, other issues.

[alexeagle]

This issue was moved to angular/angular-cli#12168