Fix Memory Leak in virQEMUCapsInitGuestFromBinary()
    
    While running qemucaps2xmltest, it was found that valgrind pointed out
    the following memory leaks:
    
    ==29896== 0 bytes in 1 blocks are definitely lost in loss record 1 of 65
    ==29896==    at 0x4A0577B: calloc (vg_replace_malloc.c:593)
    ==29896==    by 0x4C6B45E: virAllocN (viralloc.c:191)
    ==29896==    by 0x4232A9: virQEMUCapsGetMachineTypesCaps (qemu_capabilities.c:1999)
    ==29896==    by 0x4234E7: virQEMUCapsInitGuestFromBinary (qemu_capabilities.c:789)
    ==29896==    by 0x41F10B: testQemuCapsXML (qemucaps2xmltest.c:118)
    ==29896==    by 0x41FFD1: virtTestRun (testutils.c:201)
    ==29896==    by 0x41EE7A: mymain (qemucaps2xmltest.c:203)
    ==29896==    by 0x42074D: virtTestMain (testutils.c:789)
    ==29896==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)
    ==29896==
    ==29896== 0 bytes in 1 blocks are definitely lost in loss record 2 of 65
    ==29896==    at 0x4A0577B: calloc (vg_replace_malloc.c:593)
    ==29896==    by 0x4C6B45E: virAllocN (viralloc.c:191)
    ==29896==    by 0x4232A9: virQEMUCapsGetMachineTypesCaps (qemu_capabilities.c:1999)
    ==29896==    by 0x4234E7: virQEMUCapsInitGuestFromBinary (qemu_capabilities.c:789)
    ==29896==    by 0x41F10B: testQemuCapsXML (qemucaps2xmltest.c:118)
    ==29896==    by 0x41FFD1: virtTestRun (testutils.c:201)
    ==29896==    by 0x41EEA3: mymain (qemucaps2xmltest.c:204)
    ==29896==    by 0x42074D: virtTestMain (testutils.c:789)
    ==29896==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)
    
    Signed-off-by: Eric Blake <eblake@redhat.com>