cloudflare: handle init failures properly

Otherwise the process explodes with:
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x656b1b]

goroutine 1 [running]:
infra-sshfp-cf/cloudflare.(*service).FindHostByName(0xc000436600, {0xc00030c510, 0x18})
	/home/admin/sshfp-generator/cloudflare/service.go:25 +0x15b
main.main()
	/home/admin/sshfp-generator/main.go:89 +0x8d0
exit status 2
```
Due to inability to find the configured zone.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

cloudflare/repository.go

@@ -15,20 +15,26 @@ type repository struct {
 	ctx        context.Context
 }
 
-func NewRepository(token string, domain string) Repository {
+func NewRepository(token string, domain string) (Repository, error) {
 	logrus.Infof("cloudflare: Creating Repository")
 	api, err := cloudflare.NewWithAPIToken(token)
 	if err != nil {
-		logrus.Error(err)
-		return nil
+		logrus.Errorf("cloudflare: token init failure: %s", err)
+		return nil, err
 	}
 
 	id, err := api.ZoneIDByName(domain)
 	if err != nil {
-		logrus.Error(err)
-		return nil
+		logrus.Errorf("cloudflare: zone init failure: %s", err)
+		return nil, err
 	}
-	return &repository{api: api, domainId: id, domainName: domain, ctx: context.Background()}
+	repo := repository{
+		api:        api,
+		domainId:   id,
+		domainName: domain,
+		ctx:        context.Background(),
+	}
+	return &repo, nil
 }
 
 func (r *repository) FindRecords(hostname string, recordType string) ([]cloudflare.DNSRecord, error) {

main.go

@@ -41,7 +41,12 @@ func main() {
 	}
 
 	//Create cloudflare components
-	cloudflare := cloudflare.NewService(cloudflare.NewRepository(config.CloudflareToken, config.DomainName))
+	cfRepo, err := cloudflare.NewRepository(config.CloudflareToken, config.DomainName)
+	if err != nil {
+		logrus.Errorf("Failed to Init CloudFlare: %s", err)
+		os.Exit(1)
+	}
+	cloudflare := cloudflare.NewService(cfRepo)
 
 	//Create buffer to catch output from consul
 	var buf bytes.Buffer