actually log errors on saving federated attributes
actually log errors on saving federated attributes

refs FOO-2717

we used to log:

`Unable to save federated pseudonym: #<ActiveModel::BetterErrors::Errors:0x0000ffff581d2498>`

now we'll log:

`Unable to save federated pseudonym:
{:errors=>{:sis_user_id=>[{:attribute=>:sis_user_id, :type=>:taken,
:message=>"SIS ID \"user@domain.com\" is already in use"}]}}`

Change-Id: Ica921f2777012f0b8963461e6eb3c733e0164b98
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/290517
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Jacob Burroughs <8ecea6e385af5cf9f53123f5ca17fb5fd6a6d4b2@instructure.com>
Reviewed-by: Sean Scally <ceb34b930afeb707ad0575cfce0e31dce3c15014@instructure.com>
QA-Review: Ben Rinaca <55a6093a45d41fed7a0fcf1e8dbdc41f5092bc04@instructure.com>
Product-Review: Ben Rinaca <55a6093a45d41fed7a0fcf1e8dbdc41f5092bc04@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms