[yang-models]: Add yang extension to control translation configDB<->yang from YANG models.

[praveen-li]

[yang-models]: Add yang extension to control traslation configDB<->ya…

…ng from YANG models.

Changes:
1.) Added yang extensions in YANG models.
2.) Changed the translation and rev translation code to depend on yang extensions.
3.) Load yang models in test code similar to dev code.
4.) Minor changes in test files.
Signed-off-by: Praveen Chaudhary pchaudhary@linkedin.com

- What I did
Changes:
1.) Added yang extensions in YANG models.
2.) Changed the translation and rev translation code to depend on yang extensions.
3.) Load yang models in test code similar to dev code.
4.) Minor changes in test files.

- How I did it
Yang supports extension keyword, with that we can enter meta data in YANG module.
Here I have entered regular expression as extension to control translation configDB<->yang from YANG models

- How to verify it
Building package is enough since it already has required test cases for translation configDB<->yang.

pchaudha@e8879b00ab3e:/sonic$ make -f slave.mk target/python-wheels/sonic_yang_mgmt-1.0-py2-none-any.whl
SONiC Build System

Build Configuration
"CONFIGURED_PLATFORM"             : "broadcom"
"CONFIGURED_ARCH"                 : "amd64"
"SONIC_CONFIG_PRINT_DEPENDENCIES" : ""
"SONIC_BUILD_JOBS"                : "1"
"SONIC_CONFIG_MAKE_JOBS"          : "24"
"SONIC_USE_DOCKER_BUILDKIT"       : ""
"USERNAME"                        : "admin"
"PASSWORD"                        : "YourPaSsWoRd"
"ENABLE_DHCP_GRAPH_SERVICE"       : ""
"SHUTDOWN_BGP_ON_START"           : ""
"ENABLE_PFCWD_ON_START"           : ""
"INSTALL_DEBUG_TOOLS"             : ""
"ROUTING_STACK"                   : "frr"
"FRR_USER_UID"                    : "300"
"FRR_USER_GID"                    : "300"
"ENABLE_SYNCD_RPC"                : ""
"ENABLE_ORGANIZATION_EXTENSIONS"  : "y"
"HTTP_PROXY"                      : ""
"HTTPS_PROXY"                     : ""
"ENABLE_SYSTEM_TELEMETRY"         : ""
"SONIC_DEBUGGING_ON"              : ""
"SONIC_PROFILING_ON"              : ""
"KERNEL_PROCURE_METHOD"           : "build"
"BUILD_TIMESTAMP"                 : ""
"BLDENV"                          : ""
"VS_PREPARE_MEM"                  : "yes"
"ENABLE_SFLOW"                    : "y"

pchaudha@e8879b00ab3e:/sonic$ cd -

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