Fix regex bug in 36e9fd2a (which was a fix for ae30ae0b)

In PCRE regexes, (?!) is a negative look-ahead assertion,
whereas (?<!) is a negative look-behind assertion.

The previous iteration of this regex was trying to use
look-ahead as look-behind.  The net result was that the
gettingStartedUserToken= cookies were still causing
cache differentiation.  I also re-ordered things a bit
so that the look-behind is only in the Token part of the
alternation.

Change-Id: I5fa388888794ed069bbfc2cf2e411e94ad96500e