Support XFS as ebs_raid filesystem. Tweak README.

[bazbremner]

This could be generalised to a single

mkfs -t #{filesystem} #{md_device}

but this approach ensures xfs tools are available if required.

[chef-supermarket]

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[cwebberOps]

So testing against ubuntu-1204, this doesnt actually work. The chef run executes successfully but it doesnt actually properly lay down the filesystem

  * ruby_block[find md device in db_ebs_raid] action run       [2014-10-22T21:53:02+00:00] INFO: Processing ruby_block[find md device in db_ebs_raid] action run (/tmp/kitchen/cache/cookbooks/aws/providers/ebs_raid.rb line 271)
       [2014-10-22T21:53:02+00:00] INFO: Already mounted: /aws_raid
       [2014-10-22T21:53:02+00:00] INFO: Found /dev/md0
       mount: wrong fs type, bad option, bad superblock on /dev/md0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

       [2014-10-22T21:53:03+00:00] INFO: ruby_block[find md device in db_ebs_raid] called

[bazbremner]

@cwebberOps Hrm. It's been 6 months since I looked at this code and I'm not using that particular setup on AWS either. I'm pretty sure it was working and we were running it in production, but I can only assume something else was at play.

I can't guarantee when I'll get the time to look at this, but I'll have a look when I can.

[cwebberOps]

@bazbremner no worries. I totally understand.

[josegonzalez]

mkfs.xfs #{md_device} is how I normally setup the FS, so I'll test this with my change and resubmit the PR assuming everything works.

[tas50]

Since the xfs cookbook only installs xfsdump we can remove this and leave it up to the user to have a system capable of formatting and XFS volume

[iennae]

@bazbremner Thank you so much for your contribution. Apologies for the delay in merging. As we've grown the cookbook team we are working to have a much quicker turn around on these kind of things.

[bazbremner]

@iennae no problems - I've also not touched any cookbooks for a while either, such is life. Thanks for merging it!