Added support to auto discovery with SRV DNS registry (#60)

* Added support to auto discovery witih SRV

The yaml configuration has been modified to suport srv parameters.
Now the name is taken form the router identity to allow dynamic
discovery of devices based on SRV registry.

* Corrected format

* feat(collector): Added support to use custom DNS

* feat(collector): get default dns server from resolv.conf

* Remove getIdentity on the static config devices

config/config.go

@@ -29,13 +29,23 @@ type Config struct {
 
 // Device represents a target device
 type Device struct {
-	Name     string `yaml:"name"`
-	Address  string `yaml:"address"`
-	User     string `yaml:"user"`
-	Password string `yaml:"password"`
+	Name     string    `yaml:"name"`
+	Address  string    `yaml:"address,omitempty"`
+	Srv      SrvRecord `yaml:"srv,omitempty"`
+	User     string    `yaml:"user"`
+	Password string    `yaml:"password"`
 	Port	 string `yaml:"port"`
 }
 
+type SrvRecord struct {
+	Record string    `yaml:"record"`
+	Dns    DnsServer `yaml:"dns,omitempty"`
+}
+type DnsServer struct {
+	Address string `yaml:"address"`
+	Port    int    `yaml:"port"`
+}
+
 // Load reads YAML from reader and unmashals in Config
 func Load(r io.Reader) (*Config, error) {
 	b, err := ioutil.ReadAll(r)