Changes

testenv: fix OSMO_DEV_MAKE_DIR env var

When --autoreconf-in-src-copy was made the default, the make dir name
has been changed to make2 but this variable was not adjusted. Fix it.

Fixes: dacbca96 ("testenv: use --autoreconf-in-src-copy by default")
Change-Id: Ia46ebe1240806995960545afbb34e6533580f209