Adds `alphagov/lvm` module to Puppetfile

Allows for LVM drives to be created by Puppet.
Used in mounts.pp.
Adds `alphagov/puppet-ext4mount` module to Puppetfile

Used in mounts.pp to mount ext4 drive.
Adds 'alphagov/puppet-harden' module to Puppetfile

puppet-harden is a module to harden a base installation of Ubuntu.
Details at http://github.com/alphagov/puppet-harden.
Adds 'alphagov/puppet-clamav' module to Puppetfile

Allows Puppet to manage installation and updating of ClamAV.
ClamAV to be configured in clamav.pp manifest.
Merge branch 'add-puppet-modules' of github.com:alphagov/govuk_offsitebackups-puppet into add-puppet-modules