Only install the xfs related packages when needed

This requires a new option to be other, otherwise it defaults to the
original behavior of installing those xfs packages (which is harmless
and pretty quick, but if you're using ext4 then it's just noise).
Run LVM related code only if required
Don't hard code mount options
Set provisioned IOPS only when needed
Minor code alignment to improve readability
Add node[:ebs][:no_boot_config] option to disable EBS RAID boot config

The code doesn't work on Amazon Linux. We don't need it (we currently
don't shutdown or reboot these instances) so let's just hide it behind a
config option while keeping the current default behavior.