Support for createNamespace (#1226)

- createNamespace is a new attribute that can be added to helmDefaults
  or an individual release to enforce the creation of a release namespace
  during sync if the namespace does not exist. This leverages helm's
  (3.2+) --create-namespace flag for the install/upgrade command. If
  running helm < 3.2, the createNamespace attribute has no effect.

Resolves #891
Resolves #1140

pkg/exectest/helm.go

@@ -30,6 +30,7 @@ type Helm struct {
 	Diffed               []Release
 	FailOnUnexpectedDiff bool
 	FailOnUnexpectedList bool
+	Version              *helmexec.Version
 
 	UpdateDepsCallbacks map[string]func(string) error
 
@@ -161,6 +162,22 @@ func (helm *Helm) IsHelm3() bool {
 	return false
 }
 
+func (helm *Helm) GetVersion() helmexec.Version {
+	if helm.Version != nil {
+		return *helm.Version
+	}
+
+	return helmexec.Version{}
+}
+
+func (helm *Helm) IsVersionAtLeast(major int, minor int) bool {
+	if helm.Version == nil {
+		return false
+	}
+
+	return helm.Version.Major >= major && minor >= helm.Version.Minor
+}
+
 func (helm *Helm) sync(m *sync.Mutex, f func()) {
 	if m != nil {
 		m.Lock()