tests: break out command, command/agent on Travis (#6094)
tests: break out command, command/agent on Travis (#6094)

The command and command/agent packages are taking 5+ minutes on Travis
and this contributes to build timeouts. While this doesn't address
underlying issues, breaking these out can reduce re-runs until that
work is done.
burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,dvusboy/nomad