Add support for array values in extensible attributes (#88)

The client crashes when the value of an extensible attribute is an array.
This pull request tries to handle this case.
The error message when the ea is an array is:

panic: interface conversion: interface {} is []interface {}, not string

```
goroutine 1 [running]:
github.com/mhermida/infoblox-go-client.(*EA).UnmarshalJSON(0xc0000107e0, 0xc0001ac300, 0xbf, 0xc0, 0x7f64d6078110, 0xc0000107e0)
        /home/marcos/dev/go/hellogo/src/github.com/mhermida/infoblox-go-client/objects.go:552 +0x4cf
encoding/json.(*decodeState).object(0xc0000a7130, 0x8637a0, 0xc0000107e0, 0x16, 0xc0000a7158, 0xc00038ca7b)
```
The PR fixes it.

objects.go

@@ -3,6 +3,7 @@ package ibclient
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"reflect"
 )
 
@@ -546,14 +547,26 @@ func (ea *EA) UnmarshalJSON(b []byte) (err error) {
 	*ea = make(EA)
 	for k, v := range m {
 		val := v["value"]
-		if reflect.TypeOf(val).String() == "json.Number" {
+		switch valType := reflect.TypeOf(val).String(); valType {
+		case "json.Number":
 			var i64 int64
 			i64, err = val.(json.Number).Int64()
 			val = int(i64)
-		} else if val.(string) == "True" {
-			val = Bool(true)
-		} else if val.(string) == "False" {
-			val = Bool(false)
+		case "string":
+			if val.(string) == "True" {
+				val = Bool(true)
+			} else if val.(string) == "False" {
+				val = Bool(false)
+			}
+		case "[]interface {}":
+			nval := val.([]interface{})
+			nVals := make([]string, len(nval))
+			for i, v := range nval {
+				nVals[i] = fmt.Sprintf("%v", v)
+			}
+			val = nVals
+		default:
+			val = fmt.Sprintf("%v", val)
 		}
 
 		(*ea)[k] = val

objects_test.go

@@ -77,11 +77,13 @@ var _ = Describe("Objects", func() {
 			"Tenant Name":       "Engineering01",
 			"Maximum Wait Time": 120,
 			"DNS Support":       Bool(false),
+			"Routers":           []string{"10.1.2.234", "10.1.2.235"},
 		}
 		eaJSON := `{"Cloud API Owned":{"value":"True"},` +
 			`"Tenant Name":{"value":"Engineering01"},` +
 			`"Maximum Wait Time":{"value":120},` +
-			`"DNS Support":{"value":"False"}}`
+			`"DNS Support":{"value":"False"},` +
+			`"Routers":{"value":["10.1.2.234", "10.1.2.235"]}}`
 
 		Context("Marshalling", func() {
 			Context("expected JSON is returned", func() {