Ignore the final valid instruction and only flag duplicate CMD, ENTRYPOINT, and HEALTHCHECK instructions

[rcjsuen]

FROM alpine
CMD [ "executable" ]
CMD [ "executable" ]
ENTRYPOINT [ "executable" ]
ENTRYPOINT [ "executable" ]
HEALTHCHECK CMD [ "executable" ]
HEALTHCHECK CMD [ "executable" ]

Line: 2
CMD [ "executable" ]
^^^
Warning: There can only be one CMD instruction in a Dockerfile

Line: 3
CMD [ "executable" ]
^^^
Warning: There can only be one CMD instruction in a Dockerfile

Line: 4
ENTRYPOINT [ "executable" ]
^^^^^^^^^^
Warning: There can only be one ENTRYPOINT instruction in a Dockerfile

Line: 5
ENTRYPOINT [ "executable" ]
^^^^^^^^^^
Warning: There can only be one ENTRYPOINT instruction in a Dockerfile

Line: 6
HEALTHCHECK CMD [ "executable" ]
^^^^^^^^^^^
Warning: There can only be one HEALTHCHECK instruction in a Dockerfile

Line: 7
HEALTHCHECK CMD [ "executable" ]
^^^^^^^^^^^
Warning: There can only be one HEALTHCHECK instruction in a Dockerfile

We should just flag the duplicate that is not the last one as the last one is valid and will be used by the created image.