Add Anchor pattern to client.pp

The class mysql::client::install is "contained" in the mysql::client to avoid floating.
Update the Anchor pattern workaround

Add a step to the anchor pattern and add comment to clarify the need of this workaround.
Ref : http://docs.puppetlabs.com/puppet/2.7/reference/lang_containment.html#known-issues
Merge pull request #343 from Bit-Doctor/patch-1

Add Anchor pattern to client.pp