Selenium: pass -no-sandbox to Chrome under Docker

Selenium: pass -no-sandbox to Chrome under Docker

When running webdriver.io in a Jessie Docker container, the sandboxing
fails:

  Failed to move to new namespace: PID namespaces supported, Network
  namespace supported, but failed: errno = Operation not permitted

Detect whether we are in a Docker container by checking /.dockerenv and
if present append --no-sandbox to Chrome options.

Change-Id: Ie5c276d12553e4473c01b3407e0f7622e0a678e0