tests: plug leak in torture_bind_options_import_key

Summary:
Hello, this is a resend for a quick memory leak fix for one of the unit
tests, originally sent to the mailing list here:

 * https://www.libssh.org/archive/libssh/2017-07/0000017.html

Test Plan:
 * Before the fix and running the test with valgrind:

```
[simonsj@simonsj-lx5 : unittests] valgrind --leak-check=full ./torture_options >/dev/null
==93134== Memcheck, a memory error detector
==93134== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==93134== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==93134== Command: ./torture_options
==93134==
[  PASSED  ] 10 test(s).
[  PASSED  ] 1 test(s).
==93134==
==93134== HEAP SUMMARY:
==93134==     in use at exit: 80 bytes in 1 blocks
==93134==   total heap usage: 977 allocs, 976 frees, 75,029 bytes allocated
==93134==
==93134== 80 bytes in 1 blocks are definitely lost in loss record 1 of 1
==93134==    at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==93134==    by 0x41BAB0: ssh_key_new (pki.c:107)
==93134==    by 0x40DF90: torture_bind_options_import_key (torture_options.c:222)
==93134==    by 0x4E3AA3A: cmocka_run_one_test_or_fixture (cmocka.c:2304)
==93134==    by 0x4E3ACEA: cmocka_run_one_tests (cmocka.c:2412)
==93134==    by 0x4E3B036: _cmocka_run_group_tests (cmocka.c:2517)
==93134==    by 0x40E9E3: torture_run_tests (torture_options.c:276)
==93134==    by 0x40DE68: main (torture.c:1100)
==93134==
==93134== LEAK SUMMARY:
==93134==    definitely lost: 80 bytes in 1 blocks
==93134==    indirectly lost: 0 bytes in 0 blocks
==93134==      possibly lost: 0 bytes in 0 blocks
==93134==    still reachable: 0 bytes in 0 blocks
==93134==         suppressed: 0 bytes in 0 blocks
==93134==
==93134== For counts of detected and suppressed errors, rerun with: -v
==93134== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
```

 * And after:

```
[simonsj@simonsj-lx5 : unittests] valgrind --leak-check=full ./torture_options >/dev/null
==93294== Memcheck, a memory error detector
==93294== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==93294== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==93294== Command: ./torture_options
==93294==
[  PASSED  ] 10 test(s).
[  PASSED  ] 1 test(s).
==93294==
==93294== HEAP SUMMARY:
==93294==     in use at exit: 0 bytes in 0 blocks
==93294==   total heap usage: 977 allocs, 977 frees, 75,029 bytes allocated
==93294==
==93294== All heap blocks were freed -- no leaks are possible
==93294==
==93294== For counts of detected and suppressed errors, rerun with: -v
==93294== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
```

Reviewers: asn

Reviewed By: asn

Differential Revision: https://bugs.libssh.org/D3

Author: simonsj

tests/unittests/torture_options.c

@@ -219,15 +219,16 @@ static void torture_bind_options_import_key(void **state)
 {
     ssh_bind bind = *state;
     int rc;
-    ssh_key key = ssh_key_new();
     const char *base64_key;
+    ssh_key key = ssh_key_new();
 
     /* set null */
     rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_IMPORT_KEY, NULL);
     assert_int_equal(rc, -1);
     /* set invalid key */
     rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_IMPORT_KEY, key);
     assert_int_equal(rc, -1);
+    ssh_key_free(key);
 
     /* set rsa key */
     base64_key = torture_get_testkey(SSH_KEYTYPE_RSA, 0, 0);