The merge_configs action plugin is updated with an option to control
whether whitespace should be used around equal signs. The default
remains to use whitespace: only zookeeper.cfg doesn't use them.

This is to avoid issues with the zkCleanup.sh script which expects no
whitespace. The ZooKeeper documentation also uses no whitespace in
configuration file examples.

Change-Id: Ia082a1c002cc4e8b04f7696fdee827b747c6d13f
Closes-Bug: #1917490