(PUP-2950) rubocop enabling Style/AndOr cop in pops directory

This commits enables `AndOr` cop only in lib/puppet/pops directory. This cop
bans the use of `and` and `or` keywords in favor of `&&` and `||`. We have
chosen this directory as a test case to evaluate the utility of enabling
`AndOr` on the complete codebase. We inherit from the base rubocop file, so all
the other cops remain enabled. At a future date, when `AndOr` is enabled
systemwide, this file may be removed (if no other specialization exists on pops
directory).

It changes all code that uses `and` and `or` keywords to use `&&` and
`||`  instead. Note that this commit only fixes the lib/puppet/pops directory.
Further, for ease of verification of correctness, redundant parenthesis has
been used around the expressions thus converted where there was felt to be
a possibility of confusion.