Fix sign_in_page specs
Fix sign_in_page specs

A series of sign in page specs have been failing for some time
following a prior refactor.

Correct the spec helper to properly reflect that a failed sign in will
lead to the $URL/session/new page.

Fixes:
  Signing in with an unknown username fails
  Signing in with an unknown email fails
  Signing in without filling in the form fails

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