RedisPipeline ignore flush when call dtor from another thread. (sonic-net#736)

#### Why I did it
Because RedisPipeline is not thread safe, in c++ if code call exit() from another thread, the dtor of RedisPipeline will  be called from another thread and trigger a race condition issue.

#### How I did it
RedisPipeline ignore flush when call dtor from another thread.

#### How to verify it
Pass all UT and E2E test cases.

#### Which release branch to backport (provide reason below if selected)

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- Note we only backport fixes to a release branch, *not* features!
- Please also provide a reason for the backporting below.
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- [x] 202006
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- [ ] 201811
- [ ] 201911
- [ ] 202006
- [ ] 202012
- [ ] 202106
- [ ] 202111

#### Description for the changelog
RedisPipeline ignore flush when call dtor from another thread.

#### Link to config_db schema for YANG module changes
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Provide a link to config_db schema for the table for which YANG model
is defined
Link should point to correct section on https://github.com/Azure/SONiC/wiki/Configuration.
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#### A picture of a cute animal (not mandatory but encouraged)

Author: liuh-80

common/redispipeline.h

@@ -6,6 +6,11 @@
 #include "redisreply.h"
 #include "rediscommand.h"
 #include "dbconnector.h"
+#include "logger.h"
+
+#include "unistd.h"
+#include "sys/syscall.h"
+#define gettid() syscall(SYS_gettid)
 
 namespace swss {
 
@@ -19,10 +24,20 @@ class RedisPipeline {
         , m_remaining(0)
     {
         m_db = db->newConnector(NEWCONNECTOR_TIMEOUT);
+        initializeOwnerTid();
     }
 
     ~RedisPipeline() {
-        flush();
+        if (m_ownerTid == gettid())
+        {
+            // call flush from different thread will trigger race condition issue.
+            flush();
+        }
+        else
+        {
+            SWSS_LOG_NOTICE("RedisPipeline dtor is called from another thread, possibly due to exit(), Database: %s", getDbName().c_str());
+        }
+
         delete m_db;
     }
 
@@ -125,10 +140,16 @@ class RedisPipeline {
         return m_db;
     }
 
+    void initializeOwnerTid()
+    {
+        m_ownerTid = gettid();
+    }
+
 private:
     DBConnector *m_db;
     std::queue<int> m_expectedTypes;
     size_t m_remaining;
+    long int m_ownerTid;
 
     void mayflush()
     {