fix(pingEndpoint): change build type to 'oss2', use correct version

[bednar]

This PR fix the /ping endpoint:

• change build type from cloud2 to oss2
• use correct version for X-Influxdb-Version header

• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (if modified Go structs or API)
• Signed CLA (if not already signed)

[danxmoran]

These changes LGTM but seem unrelated to the originally-linked issues. I've edited the PR description to remove the links so those don't get auto-closed when this merges.