puppet: Fix puppet-lint warnings in various manifests.

Apparently, `puppet-lint` on Ubuntu trusty throws warnings for certain
quoting patterns that are OK in modern `puppet-lint`.  I believe the
old Zulip code was actually correct (i.e. the old `puppet-lint`
implementation was the problem), but it seems worth changing anyway to
suppress the warnings.

We also exclude more of puppet-apt from linting, since it's
third-party code.

tools/linter_lib/exclude.py

@@ -5,6 +5,7 @@ EXCLUDED_FILES = [
     "puppet/apt/README.md",
     "puppet/apt/manifests/backports.pp",
     "puppet/apt/manifests/params.pp",
+    "puppet/apt/manifests/release.pp",
     "puppet/apt/manifests/unattended_upgrades.pp",
     "puppet/stdlib/tests/file_line.pp",
     "static/third",