tests: 2.x still uses an embedded copy of bats

bats needs to be used differently on 2.x. The cherrypick from 3.x needs
to be adapted to use the embedded copy of bats.

Signed-off-by: Adrian Reber <areber@redhat.com>

tests/admin/lmod/lmod

@@ -1,4 +1,4 @@
-#!/usr/bin/env -S bats --report-formatter junit --formatter tap
+#!./common/bats/bin/bats
 # -*-sh-*-
 
 load ./common/test_helper_functions || exit 1