Merge changes I6c5b5a13,Ibcba4100,Iaf7444d0,Icc357561,If5af54bc

* changes:
  Remove null-checks (5/n)
  Store pending sessions as objects instead of ids (4/n)
  Let PreRebootVerificationHandler methods take a session object (3/n)
  Pass rollbackId to submitSessionToApexService() (2/n)
  Let #startPreRebootVerification take a session object (1/n)