Add support for ttl-except and hop-limit-except to the Juniper platform

[nward]

Add support for the ttl-except and hop-limit-except match conditions to the Juniper platform.

Have added tests, and all passing fine.

Have added docs.

Generates valid config.

I have created hop-limit-except as a single value rather than a range, as Juniper does not (to my knowledge) support a range for this option.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[nward]

I'm unable to sign the CLA as my org (SearchLight) because https://cla.developers.google.com/clas doesn't let me switch to another Google account I'm logged in as (I have.. 9 or so), so it does not recognise that I am the owner of the group.

I have attempted to switch accounts on https://developers.google.com and it does not take effect on the CLA URL above.

I have signed the CLA personally, and I am a Director of the org.

¯_(ツ)_/¯