Replace mocha by rspec-mocks

puppetlabs_spec_helper recommends rspec-mocks instead of mocha[1] and
it uses rspec-mocks by default instead of mocha since v 5.0.0[2]

This is the prep work to adapt to that migration.

[1] https://github.com/puppetlabs/puppetlabs_spec_helper/#mock_with
[2] 493f0cbc1c

Closes-Bug: #2004135
Change-Id: I9056254a69cf58a4b30fefa246ace64042a70af7

spec/spec_helper.rb

@@ -13,6 +13,8 @@ RSpec.configure do |c|
 
   c.module_path = File.join(fixture_path, 'modules')
   c.manifest_dir = File.join(fixture_path, 'manifests')
+
+  c.mock_with :rspec
 end
 
 at_exit { RSpec::Puppet::Coverage.report! }

spec/unit/provider/mistral_spec.rb

@@ -15,8 +15,8 @@ describe Puppet::Provider::Mistral do
 
     it 'should fail if no auth params are passed and the mistral config file does not have the expected contents' do
       mock = {}
-      Puppet::Util::IniConfig::File.expects(:new).returns(mock)
+      expect(Puppet::Util::IniConfig::File).to receive(:new).and_return(mock)
-      mock.expects(:read).with('/etc/mistral/mistral.conf')
+      expect(mock).to receive(:read).with('/etc/mistral/mistral.conf')
       expect do
         klass.mistral_credentials
       end.to raise_error(Puppet::Error, /Mistral types will not work/)
@@ -39,8 +39,8 @@ describe Puppet::Provider::Mistral do
           'password'     => 'password',
         }
       }
-      Puppet::Util::IniConfig::File.expects(:new).returns(mock)
+      expect(Puppet::Util::IniConfig::File).to receive(:new).and_return(mock)
-      mock.expects(:read).with('/etc/mistral/mistral.conf')
+      expect(mock).to receive(:read).with('/etc/mistral/mistral.conf')
       expect(klass.mistral_credentials).to eq(creds_hash)
     end