libstore: kill sandboxes before removing paths

otherwise we may end up trying to delete a temporary directory that is
still actively being written to if a derivation is killed due to other
derivations failing or the build is aborted due to a user interruption

fixes #678

Change-Id: I4678723f11bdd261b27af8784d040a787690b107

lix/libstore/build/local-derivation-goal.cc

@@ -104,9 +104,9 @@ LocalDerivationGoal::~LocalDerivationGoal() noexcept(false)
 {
     /* Careful: we should never ever throw an exception from a
        destructor. */
-    try { deleteTmpDir(false); } catch (...) { ignoreExceptionInDestructor(); }
     try { killChild(); } catch (...) { ignoreExceptionInDestructor(); }
     try { stopDaemon(); } catch (...) { ignoreExceptionInDestructor(); }
+    try { deleteTmpDir(false); } catch (...) { ignoreExceptionInDestructor(); }
 }