db_stress: improve TestGet() failure printing (#5989)

Summary:
Right now, in db_stress's CF consistency test's TestGet case, if failure happens, we do normal string printing, rather than hex printing, so that some text is not printed out, which makes debugging harder. Fix it by printing hex instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5989

Test Plan: Build db_stress and see t passes.

Differential Revision: D18363552

fbshipit-source-id: 09d1b8f6fbff37441cbe7e63a1aef27551226cec

tools/db_stress_tool.cc

@@ -4277,27 +4277,31 @@ class CfConsistencyStressTest : public StressTest {
           }
           if (!found && s.ok()) {
             fprintf(stderr, "Get() return different results with key %s\n",
-                    key_str.c_str());
+                    Slice(key_str).ToString(true).c_str());
             fprintf(stderr, "CF %s is not found\n",
                     column_family_names_[0].c_str());
             fprintf(stderr, "CF %s returns value %s\n",
-                    column_family_names_[i].c_str(), value1.c_str());
+                    column_family_names_[i].c_str(),
+                    Slice(value1).ToString(true).c_str());
             is_consistent = false;
           } else if (found && s.IsNotFound()) {
             fprintf(stderr, "Get() return different results with key %s\n",
-                    key_str.c_str());
+                    Slice(key_str).ToString(true).c_str());
             fprintf(stderr, "CF %s returns value %s\n",
-                    column_family_names_[0].c_str(), value0.c_str());
+                    column_family_names_[0].c_str(),
+                    Slice(value0).ToString(true).c_str());
             fprintf(stderr, "CF %s is not found\n",
                     column_family_names_[i].c_str());
             is_consistent = false;
           } else if (s.ok() && value0 != value1) {
             fprintf(stderr, "Get() return different results with key %s\n",
-                    key_str.c_str());
+                    Slice(key_str).ToString(true).c_str());
             fprintf(stderr, "CF %s returns value %s\n",
-                    column_family_names_[0].c_str(), value0.c_str());
+                    column_family_names_[0].c_str(),
+                    Slice(value0).ToString(true).c_str());
             fprintf(stderr, "CF %s returns value %s\n",
-                    column_family_names_[i].c_str(), value1.c_str());
+                    column_family_names_[i].c_str(),
+                    Slice(value1).ToString(true).c_str());
             is_consistent = false;
           }
           if (!is_consistent) {