update_engine: Remove usage of non-literal format string.

FakeP2PManagerConfiguration used a private variable to store a
format string that unittests can change. This implies that we use a
non-literal format string with printf.

This patch instead uses {file_id} and {minsize} as markers on that
string that get replaced later to the passed values, avoiding the
non-literal format string. This also drops the exception flag from
the gyp file.

BUG=chromium:394166
TEST=USE="clang asan" FEATURES="test" cros_workon_make update_engine

Change-Id: I071a743e756c6214f4915b094520ef73ae902362
Reviewed-on: https://chromium-review.googlesource.com/208205
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/p2p_manager_unittest.cc b/p2p_manager_unittest.cc
index 262031f..af83d4a 100644
--- a/p2p_manager_unittest.cc
+++ b/p2p_manager_unittest.cc
@@ -437,7 +437,8 @@
 
   // Emulate p2p-client returning valid URL with "fooX", 42 and "cros_au"
   // being propagated in the right places.
-  test_conf_->SetP2PClientCommandLine("echo 'http://1.2.3.4/%s_%zu'");
+  test_conf_->SetP2PClientCommandLine(
+      "echo 'http://1.2.3.4/{file_id}_{minsize}'");
   manager->LookupUrlForFile("fooX", 42, TimeDelta(),
                             base::Bind(ExpectUrl,
                                        "http://1.2.3.4/fooX.cros_au_42", loop));