Handle string credentials

Author: Clebam

lib/puppet/provider/dsc_base_provider/dsc_base_provider.rb

@@ -777,7 +777,7 @@ def prepare_credentials(resource)
       variable_name = random_variable_name
       credential_hash = {
         'user' => property_hash[:value]['user'],
-        'password' => escape_quotes(property_hash[:value]['password'].unwrap)
+        'password' => escape_quotes(unwrap(property_hash[:value]['password']))
       }
       credentials_block << format_pscredential(variable_name, credential_hash)
       instantiated_variables.merge!(variable_name => credential_hash)
@@ -908,7 +908,7 @@ def invoke_params(resource)
                                   # the Credential hash interpolable as it will be replaced by a variable reference.
                                   {
                                     'user' => property_hash[:value]['user'],
-                                    'password' => escape_quotes(property_hash[:value]['password'].unwrap)
+                                    'password' => escape_quotes(unwrap(property_hash[:value]['password']))
                                   }
                                 when 'DateTime'
                                   # These have to be handled specifically because they rely on the *Puppet* DateTime,