Fix creating keystore when upgrading

[jasontedor]

When upgrading via the RPM package, we can run into a problem where the keystore fails to be created. This arises because the %post script on RPM runs after the new package files are installed but before the removal of the old package files. This means that the contents of the lib folder can contain files from the old package and the new package and thus running the create keystore tool can encounter JAR hell issues and fail. To solve this, we move creating the keystore to the %posttrans script which runs after the old package files are removed. We only need to do this on the RPM package, so we add a switch in the shared post-install script.

Relates #28928

[elasticmachine]

Pinging @elastic/es-core-infra

[jasontedor]

@rjernst There is another solution to this problem which is to move our libs from lib to lib-${version}. Let me know what you think of this approach versus the approach proposed here. Personally I prefer the approach presented here because I do not want to have to keep reasoning through executing Elasticsearch code when the system is in a weird state with both old and new package files present. I find it easier to reason about when we do this when the system is in a clear state. However, I am open to considering the alternative approach that I propose here, as well as other approaches.

[jasontedor]

Prior to this change, installation would proceed like this:

oel-6:~$ sudo rpm -i elasticsearch-6.0.0.rpm 
warning: elasticsearch-6.0.0.rpm: Header V4 RSA/SHA512 Signature, key ID d88e42b4: NOKEY
Creating elasticsearch group... OK
Creating elasticsearch user... OK
### NOT starting on installation, please execute the following statements to configure elasticsearch service to start automatically using chkconfig
 sudo chkconfig --add elasticsearch
### You can start elasticsearch service by executing
 sudo service elasticsearch start
oel-6:~$ sudo rpm -U /elasticsearch/elasticsearch-7.0.0-alpha1-SNAPSHOT.rpm 
Exception in thread "main" java.lang.NoSuchMethodError: org.elasticsearch.cli.MultiCommand.<init>(Ljava/lang/String;Ljava/lang/Runnable;)V
	at org.elasticsearch.cli.LoggingAwareMultiCommand.<init>(LoggingAwareMultiCommand.java:36)
	at org.elasticsearch.common.settings.KeyStoreCli.<init>(KeyStoreCli.java:32)
	at org.elasticsearch.common.settings.KeyStoreCli.main(KeyStoreCli.java:41)
chown: cannot access `/etc/elasticsearch/elasticsearch.keystore': No such file or directory
chmod: cannot access `/etc/elasticsearch/elasticsearch.keystore': No such file or directory
md5sum: /etc/elasticsearch/elasticsearch.keystore: No such file or directory
warning: %post(elasticsearch-0:7.0.0_alpha1_SNAPSHOT-1.noarch) scriptlet failed, exit status 1

After this change:

oel-6:~$ sudo rpm -i elasticsearch-6.0.0.rpm 
warning: elasticsearch-6.0.0.rpm: Header V4 RSA/SHA512 Signature, key ID d88e42b4: NOKEY
Creating elasticsearch group... OK
Creating elasticsearch user... OK
### NOT starting on installation, please execute the following statements to configure elasticsearch service to start automatically using chkconfig
 sudo chkconfig --add elasticsearch
### You can start elasticsearch service by executing
 sudo service elasticsearch start
oel-6:~$ sudo rpm -U /elasticsearch/elasticsearch-7.0.0-alpha1-SNAPSHOT.rpm 
Created elasticsearch keystore in /etc/elasticsearch

[rjernst]

LGTM. I'm ok with this approach.

[jasontedor]

run packaging tests