tests: always clean the test directory

previously the test directory could have been left untouched before executing
a test when `init.sh` was not run - and sometimes it isn't
supposed to be run - which made the test suite highly stateful and thus
behaving surprisingly on multiple runs.

tests/functional/common/init.sh

@@ -1,10 +1,8 @@
 test -n "$TEST_ROOT"
-if test -d "$TEST_ROOT"; then
-    chmod -R u+rw "$TEST_ROOT"
-    # We would delete any daemon socket, so let's stop the daemon first.
-    killDaemon
-    rm -rf "$TEST_ROOT"
-fi
+# We would delete any daemon socket, so let's stop the daemon first.
+killDaemon
+# Destroy the test directory that may have persisted from previous runs
+rm -rf "$TEST_ROOT"
 mkdir -p "$TEST_ROOT"
 mkdir "$TEST_HOME"