TravisCI xenial updates

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Update to support xenial build environment in travis CI
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Tested on conrad+gnu. https://github.com/CICE-Consortium/Test-Results/wiki/6a30b42b40.conrad.gnu.190729.190930
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please provide any additional information or relevant details below:

Testing xenial which has become the default build environment on travisCI. It was failing with netcdf. The workaround is to add dist: trusty to the current setup, but this PR attempts to get things working with xenial.

For now, this PR is just providing the ability to test travis. We can decide later how to proceed, whether to stay with trusty or move to xenial, etc.

[apcraig]

This passes travisCI and I have update testing on conrad+gnu. I think we should merge this to master to allow us to run with the new build environment. Not sure how long the older env will work.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@ffee9a7). Click here to learn what that means.
The diff coverage is n/a.

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  Coverage          ?   37.75%           
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  Files             ?       59           
  Lines             ?    30640           
  Branches          ?        0           
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  Hits              ?    11567           
  Misses            ?    19073           
  Partials          ?        0

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[apcraig]

Ignore the codecov reporting. Somehow, that is happening "automatically". I am testing the codecov tools in my sandbox now for CICE. Still need to understand how git and codecov interact.

[eclare108213]

Thanks for figuring this out so quickly.