Bug#704752: uses build_alias instead of DEB_HOST_MULTIARCH for configuration

[Julian Taylor]

Package: esorex
Version: 3.9.6-1

the esorex uses build_alias for the plugin directory in the default
configuration.
This is not the same as DEB_HOST_MULTIARCH which is normally used for
architecture dependent system installations.
E.g. on i386 build_alias is i486-linux-gnu instead of i386-linux-gnu