CA-146652: xen-ringwatch generates too many false positives in crit.log

The problem arises because tapdisk3 updates a VBD's ring stats file every 5
seconds, while xen-ringwatch expects pending requests to have been completed in
1 second. This results in notifications of unserviced requests being generated
in crit.log. To address the problem we need to guarantee that 'stats' is
updated at least once per xen-ringwatch call. Thus, xen-ringwatch's timeout is
raised to 4 seconds and tapdisk3's 'stats' update interval is lowered to 3
seconds.

Change in blktap/drivers/td-blkif.c:
-   if (t - blkif->xenvbd_stats.last < 5)
+   if (t - blkif->xenvbd_stats.last < 3)

Signed-off-by: Kostas Ladopoulos <konstantinos.ladopoulos@citrix.com>
CA-149278 - Fixing listing vcpus using libxl