Revert "ci: disable osx tests until a new pyyaml is released"

[sergiusens]

pyyaml has been released and the brew formula has been updated.

This reverts commit 75c06e4.

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on bug reports?
• If this is a new feature. Have you discussed the design on the forum?
• Have you successfully run ./runtests.sh static?
• Have you successfully run ./runtests.sh tests/unit?

---

[codecov-io]

Codecov Report

Merging #2213 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2213      +/-   ##
==========================================
- Coverage   91.21%   91.21%   -0.01%     
==========================================
  Files         208      210       +2     
  Lines       13160    13318     +158     
  Branches     1957     1982      +25     
==========================================
+ Hits        12004    12148     +144     
- Misses        788      795       +7     
- Partials      368      375       +7

Impacted Files	Coverage Δ
snapcraft/internal/dirs.py	53.33% <0%> (-0.52%)	⬇️
snapcraft/internal/project_loader/_env.py	96.22% <0%> (ø)	⬆️
snapcraft/cli/templates.py	87.09% <0%> (ø)
snapcraft/internal/project_loader/_templates.py	91.17% <0%> (ø)
snapcraft/internal/project_loader/_config.py	99.52% <0%> (ø)	⬆️
snapcraft/cli/_runner.py	95.45% <0%> (+0.1%)	⬆️
snapcraft/internal/common.py	97.22% <0%> (+0.12%)	⬆️
snapcraft/internal/project_loader/__init__.py	92.3% <0%> (+0.3%)	⬆️
snapcraft/internal/project_loader/errors.py	96.15% <0%> (+0.59%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b772997...4fc27e1. Read the comment docs.

[sergiusens]

Only seeing errors in spread which are unrelated

2018-08-15 11:23:33 Failed tasks: 6
    - google:ubuntu-14.04-64:tests/spread/plugins/autotools/cross_compile
    - google:ubuntu-14.04-64:tests/spread/plugins/autotools/run
    - google:ubuntu-16.04-64:tests/spread/plugins/autotools/cross_compile
    - google:ubuntu-16.04-64:tests/spread/plugins/autotools/run
    - google:ubuntu-18.04-64:tests/spread/plugins/autotools/cross_compile
    - google:ubuntu-18.04-64:tests/spread/plugins/autotools/run
error: unsuccessful run