(PUP-643) Ignore pkg's certificate expiration warning messages

When a pkg certificate is in it's last 30 days before expiration, the
pkg tools emit a warning message so you can get a new certificate for
some operations. The 'latest' method issues a 'pkg -Hn <package>' which
trips this warning message, but the message was unexpected and 'latest'
would raise, failing the catalog application.

This commit simply ignores such certificate expiration warnings.

While I was in there, I split a very compact line of code across a couple
lines and added some spaces, in the name of readability.
(PUP-643) Report a puppet warning when pkg warns
Merge pull request #3177 from kylog/issue/stable/pup-643/pkg-skip-certificate-expiration-warnings

Issue/stable/pup 643/pkg skip certificate expiration warnings
Merge branch 'stable'

* stable:
  (PUP-643) Report a puppet warning when pkg warns
  (PUP-643) Ignore pkg's certificate expiration warning messages