There are some path where the buffer is not passed to
virCommandAddArgBuffer and therefore the buffer might leak.

==191201== 1,010 bytes in 1 blocks are definitely lost in loss record 826 of 836
==191201==    at 0x4C2CE3F: malloc (vg_replace_malloc.c:298)
==191201==    by 0x4C2F1BF: realloc (vg_replace_malloc.c:785)
==191201==    by 0x5D39E82: virReallocN (viralloc.c:245)
==191201==    by 0x5D3E8F2: virBufferGrow (virbuffer.c:150)
==191201==    by 0x5D3E9C8: virBufferAdd (virbuffer.c:185)
==191201==    by 0x56EAC98: qemuBuildFloppyCommandLineControllerOptions (qemu_command.c:2162)
==191201==    by 0x56EB3E1: qemuBuildDisksCommandLine (qemu_command.c:2370)
==191201==    by 0x570055E: qemuBuildCommandLine (qemu_command.c:10315)
==191201==    by 0x575EA7F: qemuProcessCreatePretendCmd (qemu_process.c:6777)
==191201==    by 0x113DAB: testCompareXMLToArgv (qemuxml2argvtest.c:598)
==191201==    by 0x13A75B: virTestRun (testutils.c:180)
==191201==    by 0x138BE8: mymain (qemuxml2argvtest.c:2975)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>