[orch] change Consumer class to support multiple values for the same key

[zhenggen-xu]

Description

The Consumer class is used by the orch objects to deal with the redis consumer tables' popped items. It has m_toSync map to save the tasks. During the operations (more items than the orch objects can handle), the tasks in the map is merged for optimization. However, since it is a map, we would only have one value for each key. This potentially eliminate the necessary actions from Redis, e,g, we have a DEL action and SET action coming out from Redis for some key, we would overwrite the DEL action today in the code and thus not able to delete some objects as we intended.

The PR changed the m_toSync from map to multi-map to get multiple values for one key. In this design, we keep maximun two values per key, DEL or SET or DEL+SET. We need strictly keep the order of DEL and SET. It is possible to use map of vectors to fulfill this, we chose multi-map because:
1, It will have less/no changes to different orch classes to iterate the m_toSync
2, The order can be guaranteed. The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change. (since C++11). See
https://en.cppreference.com/w/cpp/container/multimap

The PR also refactors the consumer class so vlanmgr.cpp and routeorch.cpp will leverage the Consumer functions instead of operating on the members. It also refactors the UT code (aclorch_ut.cpp) so it removes the redundant code and uses the same code.

Google UT tests were added for Consumer Class especially for different cases for addToSync() function.

What I did
Change the m_toSync in Consumer class to multimap so it could support both DEL and SET
Reload Consumer addToSync() and refactor vlanmgr/route-orch and ut code to use it
Add google ut for consumer class

Why I did it
See description.

How I verified it
Unit tests:
Running main() from gtest_main.cc

[==========] Running 19 tests from 5 test cases.
[----------] Global test environment set-up.
[----------] 1 test from AclTest
[ RUN      ] AclTest.Create_L3_Acl_Table
[       OK ] AclTest.Create_L3_Acl_Table (1 ms)
[----------] 1 test from AclTest (1 ms total)

[----------] 3 tests from AclOrchTest
[ RUN      ] AclOrchTest.ACL_Creation_and_Destorying
[       OK ] AclOrchTest.ACL_Creation_and_Destorying (1000 ms)
[ RUN      ] AclOrchTest.L3Acl_Matches_Actions
[       OK ] AclOrchTest.L3Acl_Matches_Actions (1001 ms)
[ RUN      ] AclOrchTest.L3V6Acl_Matches_Actions
[       OK ] AclOrchTest.L3V6Acl_Matches_Actions (1000 ms)
[----------] 3 tests from AclOrchTest (3003 ms total)

[----------] 2 tests from PortsOrchTest
[ RUN      ] PortsOrchTest.PortReadinessColdBoot
[       OK ] PortsOrchTest.PortReadinessColdBoot (21 ms)
[ RUN      ] PortsOrchTest.PortReadinessWarmBoot
[       OK ] PortsOrchTest.PortReadinessWarmBoot (13 ms)
[----------] 2 tests from PortsOrchTest (34 ms total)

[----------] 4 tests from SaiSpy
[ RUN      ] SaiSpy.CURD
[       OK ] SaiSpy.CURD (0 ms)
[ RUN      ] SaiSpy.Same_Function_Signature_In_Same_API_Table
[       OK ] SaiSpy.Same_Function_Signature_In_Same_API_Table (0 ms)
[ RUN      ] SaiSpy.Same_Function_Signature_In_Different_API_Table
[       OK ] SaiSpy.Same_Function_Signature_In_Different_API_Table (0 ms)
[ RUN      ] SaiSpy.create_switch_and_acl_table
[       OK ] SaiSpy.create_switch_and_acl_table (0 ms)
[----------] 4 tests from SaiSpy (0 ms total)

[----------] 9 tests from ConsumerTest
[ RUN      ] ConsumerTest.ConsumerAddToSync_Set
[       OK ] ConsumerTest.ConsumerAddToSync_Set (1 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Del
[       OK ] ConsumerTest.ConsumerAddToSync_Del (0 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Set_Del
[       OK ] ConsumerTest.ConsumerAddToSync_Set_Del (0 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Del_Set
[       OK ] ConsumerTest.ConsumerAddToSync_Del_Set (130 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Set_Del_Set_Multi
[       OK ] ConsumerTest.ConsumerAddToSync_Set_Del_Set_Multi (204 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Set_Del_Set_Multi_In_Q
[       OK ] ConsumerTest.ConsumerAddToSync_Set_Del_Set_Multi_In_Q (4 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Del_Set_Setnew
[       OK ] ConsumerTest.ConsumerAddToSync_Del_Set_Setnew (0 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Del_Set_Setnew1
[       OK ] ConsumerTest.ConsumerAddToSync_Del_Set_Setnew1 (0 ms)
[ RUN      ] ConsumerTest.ConsumerAddToSync_Ind_Set_Del
[       OK ] ConsumerTest.ConsumerAddToSync_Ind_Set_Del (0 ms)
[----------] 9 tests from ConsumerTest (340 ms total)

[----------] Global test environment tear-down
[==========] 19 tests from 5 test cases ran. (4344 ms total)
[  PASSED  ] 19 tests.

Details if related

[qiluo-msft]

Could you also change the title as a bug fix statement?

[lguohan]

i am ok with this pr.

[zhenggen-xu]

@qiluo-msft Feedback was addressed.