Initial journald log provider attempt

**What**
- journald log provider using exec to journalctl
```
journalctl -t <namespace>:<name>  --output=json --since=<timestamp> <--follow> --output-fields=SYSLOG_IDENTIFIER,MESSAGE,_PID,_SOURCE_REALTIME_TIMESTAMP
```
- This can be tested manually using `faas-cli logs` as normal, e.g.
  `faas-cli logs nodeinfo` should tail the last 5 mins of logs.
- Very basic tests ensuring that the `journalctl` comamand is correctly
  construction and that the json log entrys are parsed correctly.
- Add simple e2e test to grep the function logs

Signed-off-by: Lucas Roesler <roesler.lucas@gmail.com>

cmd/provider.go

@@ -11,9 +11,11 @@ import (
 
 	"github.com/containerd/containerd"
 	bootstrap "github.com/openfaas/faas-provider"
+	"github.com/openfaas/faas-provider/logs"
 	"github.com/openfaas/faas-provider/proxy"
 	"github.com/openfaas/faas-provider/types"
 	"github.com/openfaas/faasd/pkg/cninetwork"
+	faasdlogs "github.com/openfaas/faasd/pkg/logs"
 	"github.com/openfaas/faasd/pkg/provider/config"
 	"github.com/openfaas/faasd/pkg/provider/handlers"
 	"github.com/spf13/cobra"
@@ -93,14 +95,7 @@ func makeProviderCmd() *cobra.Command {
 			InfoHandler:          handlers.MakeInfoHandler(Version, GitCommit),
 			ListNamespaceHandler: listNamespaces(),
 			SecretHandler:        handlers.MakeSecretHandler(client, userSecretPath),
-			LogHandler: func(w http.ResponseWriter, r *http.Request) {
-				if r.Body != nil {
-					defer r.Body.Close()
-				}
-
-				w.WriteHeader(http.StatusNotImplemented)
-				w.Write([]byte(`Logs are not implemented for faasd`))
-			},
+			LogHandler:           logs.NewLogHandlerFunc(faasdlogs.New(), config.ReadTimeout),
 		}
 
 		log.Printf("Listening on TCP port: %d\n", *config.TCPPort)