Bump puppetlabs-mysql to 6.0.0

The fix that fixes the functions api to the
puppet 4 syntax is released in 6.0.0 which
causes the undefined issue [1] [2].

On this line [3] in the latest 5.x release
it should be for example mysql::deepmerge.

The Puppet change that caused this [3] and
the puppetlabs-mysql that fixes it [4]

[1] http://logs.openstack.org/46/613446/2/check/puppet-openstack-unit-5.5-centos-7/f7f3999/job-output.txt.gz#_2018-10-30_00_19_35_920695
[2] https://tickets.puppetlabs.com/browse/PUP-9270
[3] https://tickets.puppetlabs.com/browse/PUP-9137
[4] puppetlabs/puppetlabs-mysql#1044

Change-Id: Ib5ff4bd7119b8dfee91c884007c617dfaa591840

Author: tobias-urdin

Puppetfile

@@ -192,7 +192,7 @@ mod 'inifile',
 
 mod 'mysql',
   :git => 'https://github.com/puppetlabs/puppetlabs-mysql',
-  :ref => '5.4.0'
+  :ref => '6.0.0'
 
 mod 'postgresql',
   :git => 'https://github.com/puppetlabs/puppetlabs-postgresql',