Don't fail but warn when can't connect to S3

Previously it made impossible to run tests when PR was
initiated from a fork.
DRY by using get_version_from_git()
Transform version-number-gSHA1 to version-SHA1

Then 'number' part varies depending on how the repository
was cloned, giving different results for local clones and
on travis-ci.
Use .append() instead of += in examples/test
Merge pull request #1068 from ContinuumIO/mattpap/fix_s3_conn

Improvements to examples/test (S3 conn, version detection)