DRY up spec/requests/sign_up_spec section
DRY up spec/requests/sign_up_spec section

DRY up 'Create New Student Account (from teacher interface)' block
* replace instance vars w/ let()s
* replace duplicated strings w/ let()-created values
* split out 'enters the student's name correctly' &
  'enters the full name ...' contexts

ddmck/Empirical-Core,ddmck/Empirical-Core,ddmck/Empirical-Core,ddmck/Empirical-Core