The accept header was being set incorrectly to text instead of json.
Also added a defensive null check in JsonClientFilter.

Using top command instead of true so that the container keeps running
and returns the valid state

The accept header was being set incorrectly to text instead of json.
Also added a defensive null check in JsonClientFilter.

Conflicts:

src/test/java/com/github/dockerjava/client/command/StartContainerCmdTest
.java