test: Add sane default for TESTENV_ROOT; enable easier independent test runs

Signed-off-by: Jacques de Laval <jacques@de-laval.se>

test/testenv_exec.sh

@@ -11,7 +11,7 @@ target="$1"
 shift
 
 TEST_DIR=$(dirname "$0")
-TESTS_ROOT="${TESTS_ROOT:-$(pwd)/${TEST_DIR}/test-root}"
+TESTENV_ROOT="${TESTENV_ROOT:-$(pwd)/${TEST_DIR}/test-root}"
 
 nsenter=$(command -v nsenter)
 chroot=$(command -v chroot)
@@ -33,4 +33,4 @@ export PATH
     --net \
     --pid \
     -w -t "$target" \
-    "$chroot" "$TESTS_ROOT" "$@"
+    "$chroot" "$TESTENV_ROOT" "$@"