[yugabyte#6996] ybase: List the host for pending remote bootstrap

Summary:
When pending remote bootstrap assertion is raised, currently there is not much information on which host(s) is pending remote bootstrap:
```
21238 |   | F | 50.310855 | 5315 | ts_tablet_manager.cc:1599 | P PEER_B: Waited for 30.000sms. Still had 1 pending remote bootstraps
-- | -- | -- | -- | -- | -- | --
21239 | Fatal failure details written to /nfusr/centos-gcp-cloud/jenkins-worker-4b0/jenkins/jenkins-github-yugabyte-db-phabricator-73645/build/asan-clang-dynamic-ninja/yb-test-logs/tests-client__snapshot-txn-test/SnapshotTxnTest_RemoteBootstrapOnStart.fatal_failure_details.2021-01-23T01_39_12.pid5315.txt
21240 | F20210123 01:39:12 ../../src/yb/tserver/ts_tablet_manager.cc:1599] P PEER_B: Waited for 30.000sms. Still had 1 pending remote bootstraps
21241 | @ 0x7f47b08f9c34 yb::LogFatalHandlerSink::send(int, char const*, char const*, int, tm const*, char const*, unsigned long) (src/yb/util/logging.cc:474)
21242 | @ 0x7f47af1fa9c2
21243 | @ 0x7f47af1caf31
21244 | @ 0x7f47af1ceb7c
21245 | @ 0x7f47af1ce15d
21246 | @ 0x7f47c762c2ac yb::tserver::TSTabletManager::StartShutdown() (src/yb/tserver/ts_tablet_manager.cc:1599)
21247 | @ 0x7f47c75494cc yb::tserver::TabletServer::Shutdown() (src/yb/tserver/tablet_server.cc:366)
```
This revision adds host information (source address) so that troubleshooting is easier.

Test Plan: Run test suite via Jenkins

Reviewers: bogdan

Reviewed By: bogdan

Subscribers: ybase

Differential Revision: https://phabricator.dev.yugabyte.com/D10454

src/yb/tserver/ts_tablet_manager.cc

@@ -1122,7 +1122,15 @@ Status TSTabletManager::StartRemoteBootstrap(const StartRemoteBootstrapRequestPB
   // - first mark as closing
   // - then wait for num_tablets_being_remote_bootstrapped_ == 0
   ++num_tablets_being_remote_bootstrapped_;
-  auto decrement_num_rbs_se = ScopeExit([this](){
+  auto private_addr = req.source_private_addr()[0].host();
+  auto decrement_num_rbs_se = ScopeExit([this, &private_addr](){
+    {
+      std::lock_guard<RWMutex> lock(mutex_);
+      auto iter = bootstrap_source_addresses_.find(private_addr);
+      if (iter != bootstrap_source_addresses_.end()) {
+        bootstrap_source_addresses_.erase(iter);
+      }
+    }
     --num_tablets_being_remote_bootstrapped_;
   });
 
@@ -1143,6 +1151,7 @@ Status TSTabletManager::StartRemoteBootstrap(const StartRemoteBootstrapRequestPB
   scoped_refptr<TransitionInProgressDeleter> deleter;
   {
     std::lock_guard<RWMutex> lock(mutex_);
+    bootstrap_source_addresses_.emplace(private_addr);
     if (ClosingUnlocked()) {
       auto result = STATUS_FORMAT(
           IllegalState, "StartRemoteBootstrap in wrong state: $0",
@@ -1596,9 +1605,19 @@ void TSTabletManager::StartShutdown() {
   while (int remaining_rbs = num_tablets_being_remote_bootstrapped_ > 0) {
     if (waited >= next_report_time) {
       if (waited >= kMaxWait) {
+        std::string addr = "";
+        for (auto iter = bootstrap_source_addresses_.begin();
+             iter != bootstrap_source_addresses_.end();
+             iter++) {
+          if (iter == bootstrap_source_addresses_.begin()) {
+            addr += *iter;
+          } else {
+            addr += "," + *iter;
+          }
+        }
         LOG_WITH_PREFIX(DFATAL)
             << "Waited for " << waited << "ms. Still had "
-            << remaining_rbs << " pending remote bootstraps";
+            << remaining_rbs << " pending remote bootstraps: " + addr;
       } else {
         LOG_WITH_PREFIX(WARNING)
             << "Still waiting for " << remaining_rbs

src/yb/tserver/ts_tablet_manager.h

@@ -582,6 +582,7 @@ class TSTabletManager : public tserver::TabletPeerLookupIf, public tablet::Table
   std::shared_ptr<GarbageCollector> log_cache_gc_;
 
   std::shared_ptr<MemTracker> block_based_table_mem_tracker_;
+  std::unordered_set<std::string> bootstrap_source_addresses_;
 
   std::atomic<int32_t> num_tablets_being_remote_bootstrapped_{0};