remote: fix jump depends on uninitialised value

remote: fix jump depends on uninitialised value

Currently remote driver only initializes partial fields of
remote_connect_get_all_domain_stats_args. But xdr_array()
will check the uninitialised field 'doms_val'.
For safty reason, memset all fields of args is better.

Fix the following error from valgrind, like:
==30515== 1 errors in context 1 of 3:
==30515== Conditional jump or move depends on uninitialised value(s)
==30515==    at 0x85E9402: xdr_array (xdr_array.c:88)
==30515==    by 0x4FD8FC9: xdr_remote_connect_get_all_domain_stats_args (remote_protocol.c:6473)
==30515==    by 0x4FE72F2: virNetMessageEncodePayload (virnetmessage.c:350)
==30515==    by 0x4FDD21C: virNetClientProgramCall (virnetclientprogram.c:326)
==30515==    by 0x4FB4D01: callFull.isra.2 (remote_driver.c:6667)
==30515==    by 0x4FCBD45: call (remote_driver.c:6689)
==30515==    by 0x4FCBD45: remoteConnectGetAllDomainStats (remote_driver.c:7793)
==30515==    by 0x4FA0E75: virConnectGetAllDomainStats (libvirt.c:21678)
==30515==    by 0x147FD1: cmdDomstats (virsh-domain-monitor.c:2148)
==30515==    by 0x13006B: vshCommandRun (virsh.c:1915)
==30515==    by 0x12A9E1: main (virsh.c:3699)

Signed-off-by: Jincheng Miao <jmiao@redhat.com>