Process non-prefixed forms of all config settings [#9]

Trying to guess in advance which part of the config a user will put in
the `settings` section and which they'll put in `environment` is a
fool's errand. Just let everything go in either place.

The ServiceAccount field only had an `envconfig` tag (as opposed to
`split_words`) because that triggered envconfig to look for the non-
prefixed form. Now that we're finding non-prefixed forms of everything,
we can use the clearer/more concise tag.

Note that TestPopulateWithConflictingVariables isn't meant to say
"here's what behavior we *want*" so much as "here's what the behavior
*is*." I don't think one thing is any better than the other, but we
should know which one we're getting.

internal/helm/config_test.go

@@ -18,6 +18,10 @@ func TestConfigTestSuite(t *testing.T) {
 }
 
 func (suite *ConfigTestSuite) TestPopulateWithPluginPrefix() {
+	suite.unsetenv("HELM_COMMAND")
+	suite.unsetenv("UPDATE_DEPENDENCIES")
+	suite.unsetenv("DEBUG")
+
 	suite.setenv("PLUGIN_HELM_COMMAND", "execute order 66")
 	suite.setenv("PLUGIN_UPDATE_DEPENDENCIES", "true")
 	suite.setenv("PLUGIN_DEBUG", "true")
@@ -30,6 +34,33 @@ func (suite *ConfigTestSuite) TestPopulateWithPluginPrefix() {
 	suite.True(cfg.Debug)
 }
 
+func (suite *ConfigTestSuite) TestPopulateWithNoPrefix() {
+	suite.unsetenv("PLUGIN_HELM_COMMAND")
+	suite.unsetenv("PLUGIN_UPDATE_DEPENDENCIES")
+	suite.unsetenv("PLUGIN_DEBUG")
+
+	suite.setenv("HELM_COMMAND", "execute order 66")
+	suite.setenv("UPDATE_DEPENDENCIES", "true")
+	suite.setenv("DEBUG", "true")
+
+	cfg := Config{}
+	cfg.Populate()
+
+	suite.Equal("execute order 66", cfg.Command)
+	suite.True(cfg.UpdateDependencies)
+	suite.True(cfg.Debug)
+}
+
+func (suite *ConfigTestSuite) TestPopulateWithConflictingVariables() {
+	suite.setenv("PLUGIN_HELM_COMMAND", "execute order 66")
+	suite.setenv("HELM_COMMAND", "defend the jedi")
+
+	cfg := Config{}
+	cfg.Populate()
+
+	suite.Equal("defend the jedi", cfg.Command)
+}
+
 func (suite *ConfigTestSuite) setenv(key, val string) {
 	orig, ok := os.LookupEnv(key)
 	if ok {