Fix credential expirability check

Fixes a bug introduced during the refactor in
e92213c, which incorrectly inverted the
previous credential expirability checking logic. This caused errors
about being unable to cache otherwise cachable credentials.

Also changes the error log around the previous expirability check site
to no longer log the error that previously came from the `ExpiresAt()`
check; since this is now the wrong `err`, it's always `nil`.

Addresses kubernetes-sigs#776

pkg/filecache/converter.go

@@ -27,7 +27,7 @@ func (p *v2) Retrieve(ctx context.Context) (aws.Credentials, error) {
 		// Don't have account ID
 	}
 
-	if expiration, err := p.creds.ExpiresAt(); err != nil {
+	if expiration, err := p.creds.ExpiresAt(); err == nil {
 		resp.CanExpire = true
 		resp.Expires = expiration
 	}

pkg/filecache/filecache.go

@@ -251,7 +251,7 @@ func (f *FileCacheProvider) RetrieveWithContext(ctx context.Context) (credential
 			}
 		} else {
 			// credential doesn't support expiration time, so can't cache, but still return the credential
-			_, _ = fmt.Fprintf(os.Stderr, "Unable to cache credential: %v\n", err)
+			_, _ = fmt.Fprint(os.Stderr, "Unable to cache credential: credential doesn't support expiration\n")
 			err = nil
 		}
 		return V2CredentialToV1Value(credential), err