Make volume ensurable

[glorpen]

Pull Request (PR) description

Adds ensure parameter for gluster::volume type with support for present and absent values.

This Pull Request (PR) fixes the following issues

n/a

Since this diff could be hard to read, it was enough to add 2x if $ensure == 'present' and 1x exec { "gluster stop and remove ${title}": :)

[glorpen]

@ekohl Sorry for pinging you out of the blue but could you look at 3 waiting PRs? #215 , this one and #220.

[ekohl]

Looks good, but needs a rebase to fix the merge conflict. Mind also squashing the commits while you're at it?

[glorpen]

@ekohl done

[ekohl]

Thanks!

Since this diff could be hard to read, it was enough to add 2x if $ensure == 'present' and 1x exec { "gluster stop and remove ${title}": :)

Git and Github also have options to hide whitespace changes. They showed the same thing.