core-image.bbclass: Exclude openssh complementary packages

core-image.bbclass: Exclude openssh complementary packages

Openssh (main) package may be marked for installation via complementary
packages mechanism if sftp-server is installed
and this causes conflict with dropbear [Yocto #14858] [1].
Excluding openssh complementary packages if packagegroup-core-ssh-dropbear
is in PACKAGE_INSTALL fixes this issue.
To install openssh complementary packages in the images with
ssh-server-dropbear they may be added manually into the list because
they will be excluded from the installation even if corresonding class
(dev-pkg or dbg-pkgs) inherited.

[1]
Error:
 Problem: problem with installed package dropbear-2020.81-r0.core2_64
  - package dropbear-2020.81-r0.core2_64 conflicts with openssh provided by openssh-8.9p1-r0.core2_64
  - package openssh-8.9p1-r0.core2_64 conflicts with dropbear provided by dropbear-2020.81-r0.core2_64
  - package openssh-ptest-8.9p1-r0.core2_64 requires openssh, but none of the providers can be installed
  - conflicting requests
(try to add '--allowerasing' to command line to replace conflicting packages or '--skip-broken' to skip uninstallable packages)

Signed-off-by: Pavel Zhukov <pavel@zhukoff.net>
Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>