migration/multifd: Do error_free after migrate_set_error to avoid memleaks

migration/multifd: Do error_free after migrate_set_error to avoid memleaks

When error happen in multifd_send_thread, it use error_copy to set migrate error in
multifd_send_terminate_threads(). We should call error_free after it.

Similarly, fix another two places in multifd_recv_thread/multifd_save_cleanup.

The leak stack:
Direct leak of 48 byte(s) in 1 object(s) allocated from:
    #0 0x7f781af07cf0 in calloc (/lib64/libasan.so.5+0xefcf0)
    #1 0x7f781a2ce22d in g_malloc0 (/lib64/libglib-2.0.so.0+0x5322d)
    #2 0x55ee1d075c17 in error_setv /mnt/sdb/backup/qemu/util/error.c:61
    #3 0x55ee1d076464 in error_setg_errno_internal /mnt/sdb/backup/qemu/util/error.c:109
    #4 0x55ee1cef066e in qio_channel_socket_writev /mnt/sdb/backup/qemu/io/channel-socket.c:569
    #5 0x55ee1cee806b in qio_channel_writev /mnt/sdb/backup/qemu/io/channel.c:207
    #6 0x55ee1cee806b in qio_channel_writev_all /mnt/sdb/backup/qemu/io/channel.c:171
    #7 0x55ee1cee8248 in qio_channel_write_all /mnt/sdb/backup/qemu/io/channel.c:257
    #8 0x55ee1ca12c9a in multifd_send_thread /mnt/sdb/backup/qemu/migration/multifd.c:657
    #9 0x55ee1d0607fc in qemu_thread_start /mnt/sdb/backup/qemu/util/qemu-thread-posix.c:519
    #10 0x7f78159ae2dd in start_thread (/lib64/libpthread.so.0+0x82dd)
    #11 0x7f78156df4b2 in __GI___clone (/lib64/libc.so.6+0xfc4b2)

Indirect leak of 52 byte(s) in 1 object(s) allocated from:
    #0 0x7f781af07f28 in __interceptor_realloc (/lib64/libasan.so.5+0xeff28)
    #1 0x7f78156f07d9 in __GI___vasprintf_chk (/lib64/libc.so.6+0x10d7d9)
    #2 0x7f781a30ea6c in g_vasprintf (/lib64/libglib-2.0.so.0+0x93a6c)
    #3 0x7f781a2e7cd0 in g_strdup_vprintf (/lib64/libglib-2.0.so.0+0x6ccd0)
    #4 0x7f781a2e7d8c in g_strdup_printf (/lib64/libglib-2.0.so.0+0x6cd8c)
    #5 0x55ee1d075c86 in error_setv /mnt/sdb/backup/qemu/util/error.c:65
    #6 0x55ee1d076464 in error_setg_errno_internal /mnt/sdb/backup/qemu/util/error.c:109
    #7 0x55ee1cef066e in qio_channel_socket_writev /mnt/sdb/backup/qemu/io/channel-socket.c:569
    #8 0x55ee1cee806b in qio_channel_writev /mnt/sdb/backup/qemu/io/channel.c:207
    #9 0x55ee1cee806b in qio_channel_writev_all /mnt/sdb/backup/qemu/io/channel.c:171
    #10 0x55ee1cee8248 in qio_channel_write_all /mnt/sdb/backup/qemu/io/channel.c:257
    #11 0x55ee1ca12c9a in multifd_send_thread /mnt/sdb/backup/qemu/migration/multifd.c:657
    #12 0x55ee1d0607fc in qemu_thread_start /mnt/sdb/backup/qemu/util/qemu-thread-posix.c:519
    #13 0x7f78159ae2dd in start_thread (/lib64/libpthread.so.0+0x82dd)
    #14 0x7f78156df4b2 in __GI___clone (/lib64/libc.so.6+0xfc4b2)

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Message-Id: <20200506095416.26099-3-pannengyuan@huawei.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>