hydra-queue-runner: Don't unlock builds we just started

This happens if the previous iteration took more than 60 seconds.
Then the queue runner may think that builds failed to start properly
and unlock them, e.g.

build 5264936 pid 19248 died, unlocking
build 5264951 pid 19248 died, unlocking
build 5257073 pid 19248 died, unlocking
...

src/script/hydra-queue-runner

@@ -15,6 +15,8 @@ my $db = Hydra::Model::DB->new();
 
 STDOUT->autoflush();
 
+my $lastTime;
+
 #$SIG{CHLD} = 'IGNORE';
 
 
@@ -26,13 +28,7 @@ sub unlockDeadBuilds {
             my $pid = $build->locker;
             my $unlock = 0;
             if ($pid == $$) {
-                # Work around sqlite locking timeouts: if the child
+                if (!defined $lastTime || $build->starttime < $lastTime - 300) {
-                # barfed because of a locked DB before updating the
-                # `locker' field, then `locker' is still set to $$.
-                # So if after a minute it hasn't been updated,
-                # unlock the build.  !!! need a better fix for those
-                # locking timeouts.
-                if ($build->starttime + 60 < time) {
                     $unlock = 1;
                 }
             } elsif (kill(0, $pid) != 1) { # see if we can signal the process
@@ -190,6 +186,8 @@ while (1) {
         unlockDeadBuilds;
 
         checkBuilds;
+
+        $lastTime = time();
     };
     warn $@ if $@;