update-rc.d: support enable/disable options

* update-rc.d has added support of enable/disable options, which are
  expected to keep the previous configuration even after upgrade the packages.
  With support for these options, it will only create start/stop link
  when there are none, or it will keep the previous configuration.

  Our preinst uses "-f remove" to remove any links under the /etc/rcrunlevel.d
  which is conflicting behavior with disable/enable options, so remove it.

  For example, if a user disabled one service before upgrade,
  then after upgrade the service could be started. This happens because during preinst,
  all links have been deleted, then postinst may create the link to start service.

  With this change, we remove preinst and therefore keep the previous links
  so that after upgrade, if a link existed for the package, then the postinst
  will not create new start/stop links.

* remove '-f' for postinst. Previously, the keepalived recipe used 'remove'
  during postinst, so we needed the -f, but now the keepalived recipe has fixed
  this problem, so it's safe to remove '-f'.

[Yocto #12955]

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>