Add tcp/udp check connection input plugin

closes #650

plugins/inputs/net_response/README.md

@@ -0,0 +1,66 @@
+# Example Input Plugin
+
+The input plugin test UDP/TCP connections response time.
+It can also check response text.
+
+### Configuration:
+
+```
+# List of UDP/TCP connections you want to check
+[[inputs.net_response]]
+  protocol = "tcp"
+  # Server address (default IP localhost)
+  address = "github.com:80"
+  # Set timeout (default 1.0)
+  timeout = 1.0
+  # Set read timeout (default 1.0)
+  read_timeout = 1.0
+  # String sent to the server
+  send = "ssh"
+  # Expected string in answer
+  expect = "ssh"
+
+[[inputs.net_response]]
+  protocol = "tcp"
+  address = ":80"
+
+[[inputs.net_response]]
+  protocol = "udp"
+  # Server address (default IP localhost)
+  address = "github.com:80"
+  # Set timeout (default 1.0)
+  timeout = 1.0
+  # Set read timeout (default 1.0)
+  read_timeout = 1.0
+  # String sent to the server
+  send = "ssh"
+  # Expected string in answer
+  expect = "ssh"
+
+[[inputs.net_response]]
+  protocol = "udp"
+  address = "localhost:161"
+  timeout = 2.0
+```
+
+### Measurements & Fields:
+
+- net_response
+    - response_time (float, seconds)
+    - string_found (bool) # Only if "expected: option is set
+
+### Tags:
+
+- All measurements have the following tags:
+    - host
+    - port
+    - protocol
+
+### Example Output:
+
+```
+$ ./telegraf -config telegraf.conf -input-filter net_response -test
+net_response,host=127.0.0.1,port=22,protocol=tcp response_time=0.18070360500000002,string_found=true 1454785464182527094
+net_response,host=127.0.0.1,port=2222,protocol=tcp response_time=1.090124776,string_found=false 1454784433658942325
+
+```