executor: use grpc instead of netrpc as plugin protocol

* Added protobuf spec for executor
 * Seperated executor structs into their own package

plugins/executor/utils.go

@@ -0,0 +1,62 @@
+package executor
+
+import (
+	"github.com/golang/protobuf/ptypes"
+	"github.com/hashicorp/nomad/drivers/shared/executor/structs"
+	"github.com/hashicorp/nomad/plugins/executor/proto"
+)
+
+func processStateToProto(ps *structs.ProcessState) (*proto.ProcessState, error) {
+	timestamp, err := ptypes.TimestampProto(ps.Time)
+	if err != nil {
+		return nil, err
+	}
+	pb := &proto.ProcessState{
+		Pid:      int32(ps.Pid),
+		ExitCode: int32(ps.ExitCode),
+		Signal:   int32(ps.Signal),
+		Time:     timestamp,
+	}
+
+	return pb, nil
+}
+
+func processStateFromProto(pb *proto.ProcessState) (*structs.ProcessState, error) {
+	timestamp, err := ptypes.Timestamp(pb.Time)
+	if err != nil {
+		return nil, err
+	}
+
+	return &structs.ProcessState{
+		Pid:      int(pb.Pid),
+		ExitCode: int(pb.ExitCode),
+		Signal:   int(pb.Signal),
+		Time:     timestamp,
+	}, nil
+}
+
+func resourcesToProto(r *structs.Resources) *proto.Resources {
+	if r == nil {
+		return &proto.Resources{}
+	}
+
+	return &proto.Resources{
+		Cpu:      int32(r.CPU),
+		MemoryMB: int32(r.MemoryMB),
+		DiskMB:   int32(r.DiskMB),
+		Iops:     int32(r.IOPS),
+	}
+}
+
+func resourcesFromProto(pb *proto.Resources) *structs.Resources {
+	if pb == nil {
+		return &structs.Resources{}
+	}
+
+	return &structs.Resources{
+		CPU:      int(pb.Cpu),
+		MemoryMB: int(pb.MemoryMB),
+		DiskMB:   int(pb.DiskMB),
+		IOPS:     int(pb.Iops),
+	}
+}