[core] Adds #persisted? to Fog models
[core] Adds #persisted? to Fog models

Fog models have been able to use #new_record? for years to use an
ActiveRecord like interface to check for peristence of a resource.

When Rails 3 switched to using ActiveModel API this changed to
be #persisted?

This deprecates #new_record? and adds #persisted? as the first little
step to making fog models easier to use using ActiveModel API.

As discussed on the tickes, ActiveModel is not planned to become a
direct dependency for fog.

Relates to #1276

10io/fog,joshmyers/fog,petems/fog,icco/fog,github/fog,covario-cdiaz/fog,kongslund/fog,pravi/fog,TerryHowe/fog,brandondunne/fog,ManageIQ/fog,bryanl/fog,martinb3/fog,dtdream/fog,cocktail-io/fog,sideci-sample/sideci-sample-fog,adecarolis/fog,mavenlink/fog,dhague/fog,joshisa/fog,unorthodoxgeek/fog,displague/fog,backupify/fog,Programatica/fog,dustacio/fog,eLobato/fog,brilliomsinterop/fog,MSOpenTech/fog,dLobatog/fog,displague/fog,duhast/fog,nalabjp/fog,Ladas/fog,mohitsethi/fog,phillbaker/fog,pyama86/fog,brilliomsinterop/fog,github/fog,dtdream/fog,plribeiro3000/fog,backupify/fog,dLobatog/fog,mitchlloyd/fog,b0e/fog,fog/fog,seanhandley/fog,asebastian-r7/fog,lwander/fog,covario-cdiaz/fog,duhast/fog,nandhanurrevanth/fog,pravi/fog,surminus/fog,fog/fog,adecarolis/fog,NETWAYS/fog,glennpratt/fog,ack/fog,mitchlloyd/fog,12spokes/fog,kongslund/fog,joshmyers/fog,nicolasbrechet/fog,NETWAYS/fog,nandhanurrevanth/fog,seanhandley/fog,bryanl/fog,dpowell7/fog,rackspace/fog,TerryHowe/fog,sapcc/fog,b0ric/fog,eLobato/fog,runtimerevolution/fog,dustacio/fog,unorthodoxgeek/fog,nalabjp/fog,nandhanurrevanth/fog,mavenlink/fog,ack/fog,plribeiro3000/fog,adamleff/fog,Programatica/fog,papedaniel/fog,petems/fog,lwander/fog,10io/fog,surminus/fog,b0ric/fog,bdunne/fog,rackspace/fog,runtimerevolution/fog,asebastian-r7/fog,zephyrean/fog,phillbaker/fog,pyama86/fog,zephyrean/fog,glennpratt/fog,joshisa/fog,papedaniel/fog,Ladas/fog,sferik/fog,alphagov/fog,sapcc/fog,nicolasbrechet/fog,phillbaker/fog,theforeman/fog,alphagov/fog,cocktail-io/fog,brilliomsinterop/fog,SpryBTS/fog,MSOpenTech/fog,ManageIQ/fog,sideci-sample/sideci-sample-fog,icco/fog,martinb3/fog,dhague/fog,mohitsethi/fog,yyuu/fog,theforeman/fog,zephyrean/fog,yyuu/fog,SpryBTS/fog,adamleff/fog