Improve the InfluxDB through-put performance

This changes the current use of the InfluxDB client to instead use a
baked-in client that uses the fasthttp library.

This allows for significantly smaller allocations, the re-use of http
body buffers, and the re-use of the actual bytes of the line-protocol
metric representations.

plugins/outputs/influxdb/client/client.go

@@ -0,0 +1,22 @@
+package client
+
+import "io"
+
+type Client interface {
+	Query(command string) error
+
+	Write(b []byte) (int, error)
+	WriteWithParams(b []byte, params WriteParams) (int, error)
+
+	WriteStream(b io.Reader, contentLength int) (int, error)
+	WriteStreamWithParams(b io.Reader, contentLength int, params WriteParams) (int, error)
+
+	Close() error
+}
+
+type WriteParams struct {
+	Database        string
+	RetentionPolicy string
+	Precision       string
+	Consistency     string
+}