Don't leak @blockNodes in the loop.

==226576== 7,120 bytes in 60 blocks are definitely lost in loss record 122 of 125
==226576==    at 0x4835214: calloc (vg_replace_malloc.c:711)
==226576==    by 0x4950D7B: virAllocN (viralloc.c:191)
==226576==    by 0x49EB5BB: virXPathNodeSet (virxml.c:676)
==226576==    by 0x104DB67: virQEMUCapsLoadCPUModels (qemu_capabilities.c:3738)
==226576==    by 0x105510D: virQEMUCapsLoadCache (qemu_capabilities.c:3929)
==226576==    by 0x104459F: qemuTestParseCapabilities (testutilsqemu.c:498)
==226576==    by 0x1040DC9: testQemuCapsCopy (qemucapabilitiestest.c:105)
==226576==    by 0x1041F07: virTestRun (testutils.c:180)
==226576==    by 0x1040B45: mymain (qemucapabilitiestest.c:181)
==226576==    by 0x104320F: virTestMain (testutils.c:1119)
==226576==    by 0x1041149: main (qemucapabilitiestest.c:193)
Signed-off-by: NMarc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: NBjoern Walk <bwalk@linux.vnet.ibm.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>