[BK-CLIENT] Check empty ledger-parent node while deleting ledger

### Motivation

As discussed at [#4276](apache/pulsar#4276), while deleting ledger, bk-client should check parent node is empty before issuing delete request for parent znode.



Reviewers: Enrico Olivelli <eolivelli@gmail.com>, Charan Reddy Guttapalem <reddycharan18@gmail.com>, Matteo Merli <mmerli@apache.org>

This closes #2097 from rdhabalia/led_del and squashes the following commits:

f5c0ca3 [rdhabalia] return callback with ok
ede5e94 [rdhabalia] [Bk-Client] Check empty ledger-parent node while deleting ledger
d35aa22 [Charan Reddy Guttapalem] Move common placementpolicy components to TopologyAwareEnsemblePlacementPolicy.
b4ca453 [Charan Reddy Guttapalem] Move common placementpolicy components to TopologyAwareEnsemblePlacementPolicy.
aa84c7f [Charan Reddy Guttapalem] GetListOfEntriesOfLedger implementation
10859af [Matteo Merli] Added HTTP handler to expose bookie state
707ae5c [karanmehta93] ISSUE #2075: Bookieshell lastmark command isn't functional, always returning 0-0
41b39c6 [Charan Reddy Guttapalem] ISSUE #1967: make ledger creation and removal robust to zk connectionloss
973d2ab [Matteo Merli] Use pure python implementation of MurmurHash
9bb7e4b [Venkateswararao Jujjuri (JV)] Explicit error message if extent is not present on ZK (#2066)
bd699e6 [mtang01] ISSUE #2067: reduce byte[] allocation in add entry
7c62e12 [karanmehta93] ISSUE #2073: ReadOnlyBookieTest#testBookieContinueWritingIfMulti…
42e7780 [Ivan Kelly] DLog Namespace#openLog should declare LogNotFoundException
86bce12 [Yong Zhang] Migrate command `ledgermetadata`
407cb35 [Charan Reddy Guttapalem] ISSUE #1967: make ledger creation and removal robust to zk connectionloss
eaa6014 [Like] Support asynchronous fence request for V2 ReadEntryProcessor
d23b45e [Ivan Kelly] Fix typo in overview page for 4.8.2
44ee320 [Ivan Kelly] k
316b719 [Ivan Kelly] Wait for LAC update even if ledger fenced
0666215 [Yong Zhang] Migrate command `updatecookie`
6f33968 [Yong Zhang] Migrate command `triggeraudit`
60d993e [Yong Zhang] Migrate command `autorecovery`
ed008f2 [Yong Zhang] Migrate command `whoisauditor`
5b8e097 [Yong Zhang] Migrate command `Whatisinstanceid`
90c7944 [Yong Zhang] Migrate command `rebuild-db-ledger-locations-index`
848f852 [Nicolas Michael] ISSUE #2053: Bugfix for Percentile Calculation in FastCodahale Timer Implementation
06f2b6f [Yong Zhang] Migrate command `updateledgers`
7ad5849 [Yong Zhang] Migrate command `regenerate-interleaved-storage-index-file`
d4dbb6b [Dongfa,Huang] Avoid useless verify if LedgerEntryRequest completed
5c150f2 [Enrico Olivelli] Release notes for 4.9.1
1246826 [Yong Zhang] Migrate command `recover`
1d4cc71 [Yong Zhang] Migrate command `localconsistencycheck`
67f8362 [Yong Zhang] Migrate command `readledger`
bfbd6b0 [Yong Zhang] Migrate command `decommission`
d40b8b6 [Yong Zhang] Migrate command `readlog`
95d145a [Yong Zhang] Migrate command `nukeexistingcluster`
e2b1dc7 [Yong Zhang] Migrate command `listunderreplicated`
0988e12 [bd2019us] ISSUE #2023: change cached thread pool to fixed thread pool
6a6d7bb [Yong Zhang] Migrate command `initnewcluster`
c391fe5 [Yong Zhang] Migrate command `readlogmetadata`
120d677 [Yong Zhang] Migrate command `lostbookierecoverydelay`
bf66235 [Yong Zhang] Migrate command `deleteledger`
751e55f [Arvin] ISSUE #2020: close db properly to avoid open RocksDB failure at the second time
138a7ae [Yong Zhang] Migrate command `metadataformat`
b043d16 [Yong Zhang] Migrate command `listledgers`
4573285 [Ivan Kelly] Docker autobuild hook
e3d807a [Like] Fix IDE complain as there are multi choices for error code
9524a9f [Yong Zhang] Migrate command `readjournal`
6c3f33f [Yong Zhang] Fix when met unexpect entry id crashed
e35a108 [Like] Fix error message for unrecognized number-of-bookies
5902ee2 [Boyang Jerry Peng] fix potential NPE when releasing entry that is null
6aa73ce [Ivan Kelly] [RELEASE] Update website to include documentation for 4.8.2
1448d12 [Yong Zhang] Migrate command `listfilesondisk`
4de5983 [Yong Zhang] Issue #1987: Migrate command `convert-to-interleaved-storage`
468743e [Matteo Merli] In DbLedgerStorage use default values when config key is present but empty
f26a4ca [Ivan Kelly] Release notes for v4.8.2
ec2636c [Yong Zhang] Issue #1985: Migrate command `convert-to-db-storage`
8cc7239 [Yong Zhang] Issue #1982: Migrate command `bookiesanity`
fa90f01 [Yong Zhang] Issue #1980: Migrate command `ledger` from shell to bkctl

bookkeeper-server/src/main/java/org/apache/bookkeeper/util/ZkUtils.java

@@ -133,8 +133,17 @@ public static void asyncDeleteFullPathOptimistic(final ZooKeeper zk, final Strin
             public void processResult(int rc, String path, Object ctx) {
                 if (rc == Code.OK.intValue()) {
                     String parent = new File(originalPath).getParent().replace("\\", "/");
-                    asyncDeleteFullPathOptimistic(zk, parent, -1, callback, leafNodePath);
+                    zk.getData(parent, false, (dRc, dPath, dCtx, data, stat) -> {
+                        if (Code.OK.intValue() == dRc && (stat != null && stat.getNumChildren() == 0)) {
+                            asyncDeleteFullPathOptimistic(zk, parent, -1, callback, leafNodePath);
+                        } else {
+                            // parent node is not empty so, complete the
+                            // callback
+                            callback.processResult(Code.OK.intValue(), path, leafNodePath);
+                        }
+                    }, null);
                 } else {
+                    // parent node deletion fails.. so, complete the callback
                     if (path.equals(leafNodePath)) {
                         callback.processResult(rc, path, leafNodePath);
                     } else {