Add info how to build image if it's not in registry. Fixes #566

[Xarthisius]

During export check if image exists in the repository. If not, add blurb about how to build it to run-local.sh.

How to test?

1. Create a Tale
2. Export it
3. Confirm build blurb is in run-local.sh
4. Build Tale
5. Export it
6. Confirm build blurb is not in run-local.sh

Note

You'll need to add:

@@ -59,6 +59,8 @@ services:
       - "GOSU_CHOWN=/tmp/data"
       - DATAONE_URL=https://cn-stage-2.test.dataone.org/cn
       - HOSTDIR=/
+    extra_hosts:
+      - "images.local.wholetale.org:host-gateway"
     deploy:
       replicas: 1
       labels:

to docker-stack.yml in deploy-dev.

[codecov[bot]]

Codecov Report

Base: 92.79% // Head: 92.82% // Increases project coverage by +0.03% :tada:

Coverage data is based on head (547b0ab) compared to base (c97170f). Patch coverage: 91.66% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #567 +/- ## ========================================== + Coverage 92.79% 92.82% +0.03% ========================================== Files 61 61 Lines 4887 4894 +7 ========================================== + Hits 4535 4543 +8 + Misses 352 351 -1 ``` | [Impacted Files](https://codecov.io/gh/whole-tale/girder_wholetale/pull/567?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale) | Coverage Δ | | |---|---|---| | [server/lib/exporters/bag.py](https://codecov.io/gh/whole-tale/girder_wholetale/pull/567/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale#diff-c2VydmVyL2xpYi9leHBvcnRlcnMvYmFnLnB5) | `98.95% <91.66%> (+1.20%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale)

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