apmanager: Fix service_unittest.cc `sleep` call.

service_unittest.cc uses libchromeos::ProcessImpl to start a `sleep`
process, but ProcessImpl doesn't search PATH so the process was failing.
The test still succeeded in most cases because the failed process
existed as a zombie.

BUG=chromium:438274
TEST=Ran unittest.

Change-Id: I5834050dc13890545cf9124c76799cf6f1f02446
Reviewed-on: https://chromium-review.googlesource.com/232710
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: David Pursell <dpursell@chromium.org>
Commit-Queue: David Pursell <dpursell@chromium.org>
diff --git a/service_unittest.cc b/service_unittest.cc
index 5f99f7f..3a51ac2 100644
--- a/service_unittest.cc
+++ b/service_unittest.cc
@@ -25,6 +25,7 @@
 namespace {
   const int kServiceIdentifier = 1;
   const char kHostapdConfig[] = "ssid=test\n";
+  const char kBinSleep[] = "/bin/sleep";
 }  // namespace
 
 namespace apmanager {
@@ -35,7 +36,7 @@
 
   void StartDummyProcess() {
     service_.hostapd_process_.reset(new chromeos::ProcessImpl);
-    service_.hostapd_process_->AddArg("sleep");
+    service_.hostapd_process_->AddArg(kBinSleep);
     service_.hostapd_process_->AddArg("12345");
     CHECK(service_.hostapd_process_->Start());
     LOG(INFO) << "DummyProcess: " << service_.hostapd_process_->pid();