minijail: Fix -Wrange-loop-construct warning.

ToT clang is issuing following warnings:
loop variable 'profile' of type <snip> creates a copy from type
<snip> [-Werror,-Wrange-loop-construct]

Use reference type to silence the copy warning.

BUG=chromium:1055905
TEST=No more warning.

Change-Id: Iee9edebf07ed831b83d4360b1d3d8b803803ba83

minijail0_cli_unittest.cc

@@ -240,7 +240,7 @@ TEST_F(CliTest, valid_logging) {
     "syslog",
   };
 
-  for (const auto profile : profiles) {
+  for (const auto& profile : profiles) {
     argv[1] = profile;
     ASSERT_TRUE(parse_args_(argv));
   }
@@ -319,7 +319,7 @@ TEST_F(CliTest, valid_profile) {
     "minimalistic-mountns-nodev",
   };
 
-  for (const auto profile : profiles) {
+  for (const auto& profile : profiles) {
     argv[1] = profile;
     ASSERT_TRUE(parse_args_(argv));
   }