Instead of creating a Docker client and fetching an Info object
from the docker enpoint, call the "docker info" command
and populate a local dockerInfo struct from JSON output.
Also
- add unit tests.
- update import boss and bazel.
This change affects "test/e2e_node/e2e_node_suite_test.go"
as it consumes this Docker validator by calling
"system.ValidateSpec()".
cb56f91cc6