use cp and mkdir -p instead of install within source tree

use cp and mkdir -p instead of install within source tree

$(INSTALL) and $(INSTALL_DATA) try to change ownerships to root:bin when
copying tests to builddir. Presumably this is a difference in behaviour
between GNU and BSD install(1): the one in GNU coreutils doesn't try-and-fail
to change ownership if you're not root.

[Commit message added by smcv]

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=48127
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>