domaincapstest: Don't leak cpu definitions

When generating domain capabilities, we need to fake host CPU to
get reproducible result. We do this by copying a pre-existent CPU
config and setting VIR_TEST_MOCK_FAKE_HOST_CPU env variable which
is then consumed by qemucpumock. However, we forget to free the
CPU copy afterwards.

 2,196 (2,016 direct, 180 indirect) bytes in 18 blocks are definitely lost in loss record 291 of 297
    at 0x4838B86: calloc (vg_replace_malloc.c:762)
    by 0x57CB6A0: g_malloc0 (in /usr/lib64/libglib-2.0.so.0.6000.7)
    by 0x4A0F72D: virCPUDefNew (cpu_conf.c:87)
    by 0x4A0FAC7: virCPUDefCopyWithoutModel (cpu_conf.c:235)
    by 0x4A0FBBE: virCPUDefCopy (cpu_conf.c:273)
    by 0x10E3C0: testUtilsHostCpusGetDefForArch (testutilshostcpus.h:157)
    by 0x10E3C0: fakeHostCPU (domaincapstest.c:61)
    by 0x10E3C0: fillQemuCaps (domaincapstest.c:86)
    by 0x10E3C0: test_virDomainCapsFormat (domaincapstest.c:234)
    by 0x10F4BC: virTestRun (testutils.c:146)
    by 0x10DE93: doTestQemuInternal (domaincapstest.c:301)
    by 0x10E13D: doTestQemu (domaincapstest.c:332)
    by 0x1124CF: testQemuCapsIterate (testutilsqemu.c:635)
    by 0x10DCE3: mymain (domaincapstest.c:435)
    by 0x10FD8B: virTestMain (testutils.c:916)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NDaniel Henrique Barboza <danielhb413@gmail.com>

tests/domaincapstest.c

@@ -56,7 +56,7 @@ fillStringValues(virDomainCapsStringValuesPtr values, ...)
 static int
 fakeHostCPU(virArch arch)
 {
-    virCPUDefPtr cpu;
+    g_autoptr(virCPUDef) cpu = NULL;
 
     if (!(cpu = testUtilsHostCpusGetDefForArch(arch))) {
         virReportError(VIR_ERR_INTERNAL_ERROR,