RHEL does not use pkgconfig, nor does it use /usr/local/lib as default
library path. As a consequence, the config tests for qtopcua were not
able to find the open62541 build.
c3591fe77debc0eab79851bd8f0c050cd4f3f608 in qtopcua.git allows to
specify an environment variable to point to the correct location. Move
to /usr/local/lib/open62541/ on all platforms consistently.
Change-Id: I73c8076b70767553edfd793889150c584d5c33b5
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@qt.io>
Reviewed-by: Akseli Salovaara <akseli.salovaara@qt.io>
