Automatic merge from submit-queue (batch tested with PRs 41830, 42630)
Arrange for elasticsearch to shutdown cleanly
Kubernetes initiates "graceful shutdown" by sending SIGTERM to pid 1, which
is exactly what elasticsearch is expecting (good!)
The way the existing startup scripts worked however, this signal arrived at
the shell wrapper, not elasticsearch, and the shell wrapper exited,
killing the container immediately (bad!)
Before this change:
```
1 ? Ss 0:00 /bin/sh -c /run.sh
6 ? S 0:00 /bin/bash /run.sh
13 ? S 0:00 \_ /bin/su -c /elasticsearch/bin/elasticsearch elasticsearch
14 ? Ss 0:00 \_ sh -c /elasticsearch/bin/elasticsearch
15 ? Sl 19:18 \_ /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java ... org.elasticsearch.bootstrap.Elasticsearch start
```
After this change:
```
1 ? Ssl 0:29 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java ... org.elasticsearch.bootstrap.Elasticsearch start
```
17793bccb9