Commit 618a5b45

 ("rhel: Avoid logrotate error if /var/run/openvswitch
does not exist") updated the RHEL logrotate configuration.  This commit
makes similar changes for Debian, by synchronizing with the RHEL version.

In particular:

    - Indent to match logrotate.conf(5) examples.

    - Use "sharedscripts" flag, because the postrotate script only needs to
      run once regardless of the number of rotations.

    - Drop "delaycompress", because the postrotate script does make daemons
      reopen their log files.

    - Ignore errors calling vlog/reopen.

Also make similar changes to the xenserver logrotate script.  I confirmed
via Twitter that the xenserver packaging still has users.

CC: Timothy Redaelli <tredaelli@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Gurucharan Shetty <guru@ovn.org>