aws/ec2rolecreds: Fix security creds path to include trailing slash

Fixes the iamSecurityCredsPath var to include a trailing slash
preventing redirects when making requests to the EC2 Instance Metadata
service.

Fix aws#351

Author: jasdel

aws/ec2rolecreds/provider.go

@@ -102,7 +102,7 @@ type ec2RoleCredRespBody struct {
 	Message string
 }
 
-const iamSecurityCredsPath = "/iam/security-credentials"
+const iamSecurityCredsPath = "/iam/security-credentials/"
 
 // requestCredList requests a list of credentials from the EC2 service.
 // If there are no credentials, or there is an error making or receiving the request

aws/ec2rolecreds/provider_test.go

@@ -33,7 +33,7 @@ const credsFailRespTmpl = `{
 
 func initTestServer(expireOn string, failAssume bool) *httptest.Server {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if r.URL.Path == "/latest/meta-data/iam/security-credentials" {
+		if r.URL.Path == "/latest/meta-data/iam/security-credentials/" {
 			fmt.Fprintln(w, "RoleName")
 		} else if r.URL.Path == "/latest/meta-data/iam/security-credentials/RoleName" {
 			if failAssume {