The remote call actually doesn't free the arguments array so we leak
memory in case a domain list is specified. As the remote domain list
array consists only of stolen pointers from the actual domain objects
it's sufficient just to free the array.

Valgrind message:
==1081452== 64 bytes in 1 blocks are definitely lost in loss record 632 of 726
==1081452==    at 0x4C296D0: calloc (vg_replace_malloc.c:618)
==1081452==    by 0x4EA5CB4: virAllocN (viralloc.c:191)
==1081452==    by 0x505D21E: remoteConnectGetAllDomainStats (remote_driver.c:7785)
==1081452==    by 0x50081AA: virDomainListGetStats (libvirt-domain.c:11080)
==1081452==    by 0x155249: cmdDomstats (virsh-domain-monitor.c:2147)
==1081452==    by 0x12FB73: vshCommandRun (virsh.c:1935)
==1081452==    by 0x133FEB: main (virsh.c:3719)