Add TestReset to terraformMockResourceProvider

Have MockResourceProvider implement TestProvider to check that TestReset
is called by the test harness.

terraform/resource_provider_mock.go

@@ -56,6 +56,8 @@ type MockResourceProvider struct {
 	ReadDataDiffFn                 func(*InstanceInfo, *ResourceConfig) (*InstanceDiff, error)
 	ReadDataDiffReturn             *InstanceDiff
 	ReadDataDiffReturnError        error
+	TestResetCalled                bool
+	TestResetError                 error
 	StopCalled                     bool
 	StopFn                         func() error
 	StopReturnError                error
@@ -144,6 +146,14 @@ func (p *MockResourceProvider) Configure(c *ResourceConfig) error {
 	return p.ConfigureReturnError
 }
 
+func (p *MockResourceProvider) TestReset() error {
+	p.Lock()
+	defer p.Unlock()
+
+	p.TestResetCalled = true
+	return p.TestResetError
+}
+
 func (p *MockResourceProvider) Stop() error {
 	p.Lock()
 	defer p.Unlock()