This corrects the autobake on Stretch

Caused by commit 0268b871
and commit 3d16e0e1.

For very strange reasons (still a mistery) the above commits caused the
federatedx, archive and blackhole plugins to be missing in the
install location even though they where built in the build log.

This only occured on Stretch and not recent Ubuntu and Debian
distros.

The stretch autobake output contained:

dh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_archive.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_archive.so
dh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_blackhole.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_blackhole.so
dh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_federatedx.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_federatedx.sodh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_archive.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_archive.so
dh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_blackhole.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_blackhole.so
dh_install: Cannot find (any matches for) "usr/lib/mysql/plugin/ha_federatedx.so" (tried in "." and "debian/tmp")
dh_install: mariadb-server-10.5 missing files: usr/lib/mysql/plugin/ha_federatedx.so