block/rbd: fix memory leak in qemu_rbd_connect()

block/rbd: fix memory leak in qemu_rbd_connect()

In qemu_rbd_connect(), 'mon_host' is allocated by qemu_rbd_mon_host()
using g_strjoinv(), but it's only freed in the error path, leaking
memory in the success path as reported by valgrind:

  80 bytes in 4 blocks are definitely lost in loss record 5,028 of 6,516
     at 0x4839809: malloc (vg_replace_malloc.c:307)
     by 0x5315BB8: g_malloc (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x532B6FF: g_strjoinv (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x87D07E: qemu_rbd_mon_host (rbd.c:538)
     by 0x87D07E: qemu_rbd_connect (rbd.c:562)
     by 0x87E1CE: qemu_rbd_open (rbd.c:740)
     by 0x840EB1: bdrv_open_driver (block.c:1528)
     by 0x8453A9: bdrv_open_common (block.c:1802)
     by 0x8453A9: bdrv_open_inherit (block.c:3444)
     by 0x8464C2: bdrv_open (block.c:3537)
     by 0x8108CD: qmp_blockdev_add (blockdev.c:3569)
     by 0x8EA61B: qmp_marshal_blockdev_add (qapi-commands-block-core.c:1086)
     by 0x90B528: do_qmp_dispatch_bh (qmp-dispatch.c:131)
     by 0x907EA4: aio_bh_poll (async.c:164)

Fix freeing 'mon_host' also when qemu_rbd_connect() ends correctly.

Fixes: 0a55679b4a5061f4d74bdb1a0e81611ba3390b00
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20210329150129.121182-2-sgarzare@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>