[loadbalancer] add timeout to ApertureEagerConnections

# Problem
ApertureEagerConnections object has a semaphore which is shared by all services.
If a service is misconfigured and blocks the semaphore - all other services suffer.
Plus this can lead to OutOfMemory, because the semaphore queue is unbounded.

# Solution
Add a conservative timeout.

JIRA Issues: MEDIASERV-18729

Differential Revision: https://phabricator.twitter.biz/D1249464

Author: aivanovx

finagle-core/src/main/scala/com/twitter/finagle/loadbalancer/aperture/ApertureEagerConnections.scala

@@ -2,7 +2,10 @@ package com.twitter.finagle.loadbalancer.aperture
 
 import com.twitter.concurrent.AsyncSemaphore
 import com.twitter.finagle.stats.FinagleStatsReceiver
-import com.twitter.util.{Future, Time}
+import com.twitter.finagle.util.DefaultTimer
+import com.twitter.util.Duration
+import com.twitter.util.Future
+import com.twitter.util.Time
 
 private[aperture] object ApertureEagerConnections {
   // exposed for testing
@@ -24,6 +27,9 @@ private[aperture] object ApertureEagerConnections {
       latencyStat.add(dur)
 
       task
+      // A conservative timeout to prevent a misconfigured service
+      // from blocking all other services
+        .raiseWithin(Duration.fromSeconds(60))(DefaultTimer)
     }
   }
 }