Travis CI: Adapt configuration to Ubuntu Xenial

[Ryan J Ollos]

Necessary changes are described ​here.

[Ryan J Ollos]

This branch ​passes, but there may be a better way to do some things.

• Before adding system_site_packages: true, I was seeing a failure:

  Traceback (most recent call last):
    File "<string>", line 1, in <module>
    File "/home/travis/virtualenv/python2.7.15/lib/python2.7/site-packages/svn/core.py", line 26, in <module>
      from libsvn.core import *
    File "/home/travis/virtualenv/python2.7.15/lib/python2.7/site-packages/libsvn/core.py", line 28, in <module>
      _core = swig_import_helper()
    File "/home/travis/virtualenv/python2.7.15/lib/python2.7/site-packages/libsvn/core.py", line 20, in swig_import_helper
      import _core
  ImportError: No module named _core
  

  I couldn't determine the cause, and I can't reproduce in an Ubuntu 16.04 virtual machine, where creating the symbolic links for the svn and libsvn directories succeeds. The system_site_packages doesn't work with Python 2.6 on Trusty:

  Setting environment variables from .travis.yml
  $ export tracdb=
  0.00s$ source ~/virtualenv/python2.6_with_system_site_packages/bin/activate
  /home/travis/.travis/functions: line 104: /home/travis/virtualenv/python2.6_with_system_site_packages/bin/activate: No such file or directory
  The command "source ~/virtualenv/python2.6_with_system_site_packages/bin/activate" failed and exited with 1 during .
  Your build has been stopped.
  

• There might be a way to use source: deadsnakes and install python2.6 on Xenial, but the job fails before it even gets to installing from sources:

  Worker information
  hostname: 163d9006-81ab-4d12-9c08-2427e13655de@1.production-1-worker-org-gce-rxdx
  version: v6.2.0 https://github.com/travis-ci/worker/tree/5e5476e01646095f48eec13196fdb3faf8f5cbf7
  instance: travis-job-69dee697-71c6-4961-81da-c5b416a02988 travis-ci-sardonyx-xenial-1553530528-f909ac5 (via amqp)
  startup: 6.494757605s
  system_info
  Build system information
  Build language: python
  Build group: stable
  Build dist: xenial
  Build id: 522026938
  Job id: 522026939
  Runtime kernel version: 4.15.0-1028-gcp
  travis-build version: d0a0ac852
  Build image provisioning date and time
  Mon Mar 25 16:43:24 UTC 2019
  Operating System Details
  Distributor ID:	Ubuntu
  Description:	Ubuntu 16.04.6 LTS
  Release:	16.04
  Codename:	xenial
  Systemd Version
  systemd 229
  Cookbooks Version
  42e42e4 https://github.com/travis-ci/travis-cookbooks/tree/42e42e4
  git version
  git version 2.21.0
  bash version
  GNU bash, version 4.3.48(1)-release (x86_64-pc-linux-gnu)
  gcc version
  gcc (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609
  docker version
  Client:
   Version:           18.06.0-ce
   API version:       1.38
   Go version:        go1.10.3
   Git commit:        0ffa825
   Built:             Wed Jul 18 19:11:02 2018
   OS/Arch:           linux/amd64
   Experimental:      false
  Server:
   Engine:
    Version:          18.06.0-ce
    API version:      1.38 (minimum version 1.12)
    Go version:       go1.10.3
    Git commit:       0ffa825
    Built:            Wed Jul 18 19:09:05 2018
    OS/Arch:          linux/amd64
    Experimental:     false
  clang version
  ...
  2.6 is not installed; attempting download
  Downloading archive: https://storage.googleapis.com/travis-ci-language-archives/python/binaries/ubuntu/16.04/x86_64/python-2.6.tar.bz2
  0.13s$ curl -sSf -o python-2.6.tar.bz2 ${archive_url}
  curl: (22) The requested URL returned error: 404 Not Found
  Unable to download 2.6 archive. The archive may not exist. Please consider a different version.
  

  Alternatively, there may be a way to use pyenv to install Python 2.6.

[Ryan J Ollos]

Committed to 1.0-stable in r16909, r16910. Merged to 1.2-stable in r16911, r16912, merged to trunk in r16913, r16914.

The builds are currently using Trusty, but these changes should prepare us for when Travis CI starts deploying images with Xenial.

In the future I will look into using pyenv for the Linux configurations.

[Ryan J Ollos]

In r16928, fixed mispelling in r16911. Merged in r16929.