CLI tool: MultiCommand must override close method and close subcommands to close resources properly

[bizybot]

Elasticsearch version (bin/elasticsearch --version): All versions

Plugins installed: NA

JVM version (java -version): 9.0.1

OS version (uname -a if on a Unix-like system): Darwin MBP 17.4.0 Darwin Kernel Version 17.4.0: Sun Dec 17 09:19:54 PST 2017; root:xnu-4570.41.2~1/RELEASE_X86_64 x86_64

Description of the problem including expected versus actual behavior:
MultiCommand must override close method calling close method on subcommands to close resources
properly

Steps to reproduce:
Look at the source code of MultiCommand, close method is not overridden.

Provide logs (if relevant): NA

[elasticmachine]

Pinging @elastic/es-core-infra