bhyvexml2xmltest: Avoid leaking driver caps

bhyvexml2xmltest: Avoid leaking driver caps

Driver capabilities are allocated at the beginning of mymain(),
but roughly in the middle the architecture is switched to aarch64
and capabilities are constructed again. Without freeing the old
ones.

704 (288 direct, 416 indirect) bytes in 1 blocks are definitely lost in loss record 328 of 332
   at 0x4885098: calloc (vg_replace_malloc.c:1682)
   by 0x4EE35CA: g_malloc0 (in /usr/local/lib/libglib-2.0.so.0.8400.4)
   by 0x53314B8: g_type_create_instance (in /usr/local/lib/libgobject-2.0.so.0.8400.4)
   by 0x531A263: ??? (in /usr/local/lib/libgobject-2.0.so.0.8400.4)
   by 0x531975E: g_object_new (in /usr/local/lib/libgobject-2.0.so.0.8400.4)
   by 0x4AA9AB6: virObjectNew (virobject.c:252)
   by 0x4AF0BBA: virCapabilitiesNew (capabilities.c:87)
   by 0x401797B: virBhyveCapsBuild (bhyve_capabilities.c:51)
   by 0x4012F57: mymain (bhyvexml2xmltest.c:60)
   by 0x4016872: virTestMain (testutils.c:913)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Roman Bogorodskiy <bogorodskiy@gmail.com>