Instead of breaking up package installations and removals into separate
tasks, this patch moves them all under one task that does two execution
steps.
In addition, the security_enable_chrony variable was added to control the
installation and configuration of chrony. The tox tests for the role were
configured to skip chrony in the gate using a skipped tag, but this caused
the package install/removal task to get skipped.
Docs/release notes are included for the chrony change.
Change-Id: I1def033953b50be3911cd932fd17b10dd2c658b7
784a38ec4c