Provide a better error message when an invalid ID is given to arc patch
Provide a better error message when an invalid ID is given to arc patch

Summary:
Fixes T8937. Previously when running `arc patch D9999999999` or `arc export --revision 99999999` with a non-existent diff or revision ID you would get a rather unhelpful error message. Now you'll get a slightly more helpful error message:
```
$ arc patch D99999999
Exception
Couldn't find a revision or diff that matches the given ID
(Run with `--trace` for a full exception trace.)
```

Test Plan: Ran arc patch with a valid revision and saw it patch successfully. Ran again with an invalid revision, saw the error message.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley, yelirekim

Maniphest Tasks: T8937

Differential Revision: https://secure.phabricator.com/D17325

Khan/arcanist,codelabs-ch/arcanist,chundongwang/arcanist,codelabs-ch/arcanist,fivestars/arcanist,r4nt/arcanist,fivestars/arcanist,folsom-labs/arcanist,folsom-labs/arcanist,r4nt/arcanist,chundongwang/arcanist,phacility/arcanist,codelabs-ch/arcanist,chundongwang/arcanist,uber/arcanist,chundongwang/arcanist,fivestars/arcanist,phacility/arcanist,phacility/arcanist,Khan/arcanist,uber/arcanist,phacility/arcanist,Khan/arcanist,aik099/arcanist,codelabs-ch/arcanist,folsom-labs/arcanist,r4nt/arcanist,phacility/arcanist,aik099/arcanist,aik099/arcanist,r4nt/arcanist,aik099/arcanist,uber/arcanist,Khan/arcanist,codelabs-ch/arcanist,folsom-labs/arcanist,uber/arcanist,fivestars/arcanist