If previous test run times are provided, use them to order tests

Parallel tests should optimally be run from longest to shortest, to
minimize leftover time at the tail end of the testsuite.  If
previous-test-timing information is passed, use it to order tests:
  * Unknown tests go first, as they may be long
  * Otherwise, order by test length, longest to shortest
  * Finally, fall back to asciibetical

lib/Smokingit/Worker.pm

@@ -99,6 +99,7 @@ sub run_tests {
     my $env     = $request->{env} || '';
     my $jobs    = $request->{parallel} ? $self->max_jobs : 1;
     my $tests   = $request->{test_glob} || 't/*.t';
+    my $prev    = $request->{previous};
 
     my $result = { smoke_id => $request->{smoke_id} };
 
@@ -182,10 +183,19 @@ sub run_tests {
             if $ret;
     }
 
+    # Figure out test order
+    my @tests = glob($tests);
+    if ($prev) {
+        # Put unknown tests first (alphabetically), followed by the
+        # rest, slowest to fastest.
+        @tests = sort { (defined($prev->{$a}) <=> defined($prev->{$b}))
+                     or (    ($prev->{$b}||0) <=> ($prev->{$a}||0)    )
+                     or (                  $a cmp $b                  )
+                    } @tests;
+    }
 
     # Progress indicator via Gearman
     my $done = 0;
-    my @tests = glob($tests);
     my $harness = TAP::Harness::AnyEvent->new( {
             jobs       => $jobs,
             lib        => [".", "lib"],