* master: (158 commits)
Document the hack
Refactor property placeholder use of env. vars
Force java9 log4j hack in testing
Fix log4j buggy java version detection
Make java9 work again
Don't mkdir directly in deb init script
Fix env. var placeholder test so it's reproducible
Remove ScriptMode class in favor of boolean true/false
[rest api spec] fix doc urls
Netty request/response tracer should wait for send
Filter client/server VM options from jvm.options
[rest api spec] fix url for reindex api docs
Remove use of a Fields class in snapshot responses that contains x-content keys, in favor of declaring/using the keys directly.
Limit retries of failed allocations per index (#18467)
Proxy box method to use valueOf.
Use the build-in valueOf method instead of the custom one.
Fixed tests and added a comment to the box method.
Fix boxing.
Do not decode path when sending error
Fix race condition in snapshot initialization
...
ad7229fe72