MB-54490: Allow backup persistence cursor stats to be ignored

Occasionally, when the flusher is running and stats for checkpoint are
requested, a backup cursor will also exist. This patch introduces a
regex pattern that will ignore "persistence-backup" stats and prevent
a 'stats error' from being returned.

Change-Id: I62c8bd11a4c2cfc89de62cf821dcd8cfe909b341
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/203929
Reviewed-by: Vesko Karaganev <[email protected]>
Tested-by: Mohammad Zaeem <[email protected]>

Author: mohammadzaeem

engines/ep/tests/ep_testsuite.cc

@@ -7468,6 +7468,8 @@ static enum test_result test_mb19687_fixed(EngineIface* h) {
     // for variable keys:
     std::map<std::string_view, std::vector<std::regex> > statsPatterns{
             {"hash", {std::regex{"vb_0:histo_\\d+,\\d+"}}},
+            {"checkpoint", {std::regex{"vb_0:persistence-backup:[a-z_]+"}}},
+            {"checkpoint 0", {std::regex{"vb_0:persistence-backup:[a-z_]+"}}},
             {"kvtimings",
              {std::regex{"ro_[0-3]:readTime_\\d+,\\d+"},
               std::regex{"ro_[0-3]:readSize_\\d+,\\d+"},