Change user update to use #fetch for defaults

This changes the use of the || operator when setting the default of the
user attribute if the key does not exist to #fetch. This will make sure
that if false is passed in as the value it will still fail and use the
default setting.

This also adds constants to define and array and a hash of symbols which
is iterated over to set the users attributes.
Merge pull request #1847 from nickborromeo/refactor-user-updater

Change user update to use #fetch for defaults