Fix puppetlabs/mysql dependency in metadata.json

Recent version of puppetlabs/mysql [1] have removed the
legacy (old API) function mysql_password and now expose
it via the modern Ruby functions API [2].

with the modern functions API, "if a module has a list
of dependencies in its metadata.json file, it loads custom
functions only from those specific dependencies." [3]

Since puppet-tripleo explicitly calls mysql_password,
we now have to fix metadata.json to explicit the
dependency on puppetlabs/mysql.

Related-Bug: #1878153

[1] 39b7bdef1a
[2] https://puppet.com/docs/puppet/5.5/functions_basics.html
[3] https://puppet.com/docs/puppet/5.5/lang_write_functions_in_puppet.html#calling-a-function

Change-Id: I5a89d0bf25c7973a69ee31d3dee6dc8151a9b1e2

metadata.json

@@ -23,6 +23,7 @@
   ],
   "dependencies": [
     { "name": "puppetlabs/stdlib", "version_requirement": ">= 5.0.0 < 6.0.0" },
+    { "name": "puppetlabs/mysql", "version_requirement": ">= 5.0.0" },
     { "name": "openstack/openstacklib", "version_requirement": ">=15.0.0 <16.0.0" }
   ]
 }