Alternate SNMP plugin (#1389)

* Add a new and improved snmp plugin

* update gosnmp for duplicate packet fix

https://github.com/soniah/gosnmp/issues/68
https://github.com/soniah/gosnmp/pull/69

plugins/inputs/snmp/testdata/test.mib

@@ -0,0 +1,51 @@
+TEST DEFINITIONS ::= BEGIN
+
+testOID ::= { 1 0 0 }
+
+testTable OBJECT-TYPE
+	SYNTAX SEQUENCE OF testTableEntry
+	MAX-ACCESS not-accessible
+	STATUS current
+	::= { testOID 0 }
+
+testTableEntry OBJECT-TYPE
+	SYNTAX TestTableEntry
+	MAX-ACCESS not-accessible
+	STATUS current
+	INDEX {
+		server
+	}
+	::= { testTable 1 }
+
+TestTableEntry ::=
+	SEQUENCE {
+		server OCTET STRING,
+		connections  INTEGER,
+		latency  OCTET STRING,
+	}
+
+server OBJECT-TYPE
+	SYNTAX OCTET STRING
+	MAX-ACCESS read-only
+	STATUS current
+	::= { testTableEntry 1 }
+
+connections OBJECT-TYPE
+	SYNTAX INTEGER
+	MAX-ACCESS read-only
+	STATUS current
+	::= { testTableEntry 2 }
+
+latency OBJECT-TYPE
+	SYNTAX OCTET STRING
+	MAX-ACCESS read-only
+	STATUS current
+	::= { testTableEntry 3 }
+
+hostname OBJECT-TYPE
+	SYNTAX OCTET STRING
+	MAX-ACCESS read-only
+	STATUS current
+	::= { testOID 1 1 }
+
+END