This fix tries to address the issue in 25404 where updating environmental
variable in `service update --env-add` will not work.
The issue is because `--env-add` will only append the env, not update if
the same env already exist.
This fix tracks the env variable with a map and update if the variable
is the same.
An integration test has been added.
This fix fixes 25404.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
(cherry picked from commit c6de8add5fd5443aa820adbcd3c9a438df78823f)
Signed-off-by: Tibor Vass <tibor@docker.com>
fdf513e99d