Fix various leaks in test-system-prompt

https://bugzilla.gnome.org/show_bug.cgi?id=738508
Free GcrPkcs11Importer::queue in dispose()

Its content is freed by emptying it, but the main data structure
must be freed too with g_queue_free().

https://bugzilla.gnome.org/show_bug.cgi?id=738508
gcr-pkcs11-importer: Unref GcrImporterData::importer

'importer' must be unref'ed when no longer used otherwise
it will be leaked.

https://bugzilla.gnome.org/show_bug.cgi?id=738508
system-prompt: Fix GVariant leak

g_variant_get_variant() is (transfer full) so we need to release
the reference we get when it's no longer needed.

This fixes leak reports from valgrind similar to:

==19651== 168 (80 direct, 88 indirect) bytes in 2 blocks are definitely lost in loss record 1,137 of 1,207
==19651==    at 0x4A06BCF: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==19651==    by 0x5DE1887: g_malloc (gmem.c:97)
==19651==    by 0x5DFA5B5: g_slice_alloc (gslice.c:1007)
==19651==    by 0x5E21B14: g_variant_alloc (gvariant-core.c:476)
==19651==    by 0x5E21BA4: g_variant_new_from_bytes (gvariant-core.c:512)
==19651==    by 0x5E194F4: g_variant_new_from_trusted (gvariant.c:295)
==19651==    by 0x5E19785: g_variant_new_int32 (gvariant.c:459)
==19651==    by 0x5431FDC: parse_value_from_blob (gdbusmessage.c:1512)
==19651==    by 0x5432A7C: parse_value_from_blob (gdbusmessage.c:1850)
==19651==    by 0x5432A7C: parse_value_from_blob (gdbusmessage.c:1850)
==19651==    by 0x54327E4: parse_value_from_blob (gdbusmessage.c:1770)
==19651==    by 0x543267D: parse_value_from_blob (gdbusmessage.c:1723)
==19651==    by 0x54328EB: parse_value_from_blob (gdbusmessage.c:1804)
==19651==    by 0x543322E: g_dbus_message_new_from_blob (gdbusmessage.c:2146)
==19651==    by 0x543F246: _g_dbus_worker_do_read_cb (gdbusprivate.c:750)
==19651==    by 0x53B22C6: g_simple_async_result_complete (gsimpleasyncresult.c:763)
==19651==    by 0x53B22F8: complete_in_idle_cb (gsimpleasyncresult.c:775)
==19651==    by 0x5DDBC89: g_idle_dispatch (gmain.c:5367)
==19651==    by 0x5DD9392: g_main_dispatch (gmain.c:3111)
==19651==    by 0x5DDA118: g_main_context_dispatch (gmain.c:3710)
==19651==    by 0x5DDA30A: g_main_context_iterate (gmain.c:3781)
==19651==    by 0x5DDA731: g_main_loop_run (gmain.c:3975)
==19651==    by 0x543E6E8: gdbus_shared_thread_func (gdbusprivate.c:273)
==19651==    by 0x5E07B1C: g_thread_proxy (gthread.c:764)
==19651==    by 0x3899207529: start_thread (pthread_create.c:310)
==19651==    by 0x3898F0077C: clone (clone.S:109)

https://bugzilla.gnome.org/show_bug.cgi?id=738508
Free GcrParser::filename in ::finalize()

https://bugzilla.gnome.org/show_bug.cgi?id=738508
Don't leak GcrParsing in gcr_parser_parse_stream()

https://bugzilla.gnome.org/show_bug.cgi?id=738508
test-certificate-chain: Add missing cleanup in teardown()

This was reported as memory leaks by valgrind.

https://bugzilla.gnome.org/show_bug.cgi?id=738508
system-prompter: Add missing word to debug messages

https://bugzilla.gnome.org/show_bug.cgi?id=738508