tests/cli: escape filenames in TestBadname logs

I just got this message (not reproducible) with unescaped
binary garbage.

  UnmountErr: "/var/tmp/gocryptfs-test-parent-1026/114471933/TestMountBackground.899727687.mnt" was not found in MountInfo, cannot check for FD leaks
  UnmountErr: "/var/tmp/gocryptfs-test-parent-1026/114471933/TestConfigPipe.212912444.mnt" was not found in MountInfo, cannot check for FD leaks
  DecryptName "mzaZRF9_0IU-_5vv2wPC_i": unPad16 error: Padding too long, padLen=49 > 16
  OpenDir ".": invalid entry "KqQ346cuOAFHv_qSta5PhAwrongPattern": bad message
  DecryptName "mzaZRF9_0IU-_5vv2wP_in": unPad16 error: Padding byte at i=10 is invalid
  --- FAIL: TestBadname (0.11s)
      cli_test.go:885: Case 5 failed: 'KqQ346cuOAFHv_qSta5P_invalid_file GOCRYPTFS_BAD_NAME' in [file_invalid_file GOCRYPTFS_BAD_NAME,file,mzaZRF9_0IU-_5vv2wPC_invalid_file GOCRYPTFS_BAD_NAME,file GOCRYPTFS_BAD_NAME,�*A���y���Gfnvalid_file GOCRYPTFS_BAD_NAME,mzaZRF9_0IU-_5vv2wP_invalid_file GOCRYPTFS_BAD_NAME]
  Invalid cipherdir: directory /var/tmp/gocryptfs-test-parent-1026/114471933/TestInitNotEmpty not empty
  FAIL
  FAIL	github.com/rfjakob/gocryptfs/tests/cli	4.817s

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/cli/cli_test.go b/tests/cli/cli_test.go
index 33c9e7b..8728622 100644
--- a/tests/cli/cli_test.go
+++ b/tests/cli/cli_test.go
@@ -882,7 +882,7 @@ func TestBadname(t *testing.T) {
 
 	for i := 0; i < len(results); i++ {
 		if !results[i] {
-			t.Errorf("Case %d failed: '%s' in [%s]", i+1, searchstrings[i], strings.Join(names, ","))
+			t.Errorf("Case %d failed: %q in [%q]", i+1, searchstrings[i], strings.Join(names, ","))
 		}
 	}
 }