Make the XFS support optional, not required.

With the xfs_growfs command required, the provider was failing
suitability tests and unavailable if the xfs_growfs command was not
installed:

debug: Puppet::Type::Logical_volume::ProviderLvm: file xfs_growfs does
not exist
err: Could not find a suitable provider for logical_volume
Merge pull request #42 from smithj4/xfs-optional

Make the XFS support optional, not required.
Fix issue 16174 (http://projects.puppetlabs.com/issues/16174)

On RHEL 5 family systems ext4 filesystems can not be resized using resize2fs.
resize4fs from e4fsprogs (rpm -ql e2fsprogs|grep resize) is required.
Check if resizef4s exists, if so use it to resize ext4 instead of resize2fs
Merge pull request #47 from mkrakowitzer/mkrakowitzer/issue_16174_resize4fs_ext4_rhel5

Fix issue 16174 (http://projects.puppetlabs.com/issues/16174)
Use fully qualified volume paths
Implement 'instances' method for all LVM resources

This method makes it possible to use constructs like:
  resources { 'physical_volume': purge => true, noop => true, }
  resources { 'logical_volume':  purge => true, noop => true, }
  resources { 'volume_group':    purge => true, noop => true, }
Implement empty 'extents' method

It is required by 'instances' method.
There is no simple way to get LV size in extents,
so leave it empty for now.
Set default LV unit size to MB