Clean up provisioned modules on error; refactor Run(); add Validate()

Modules that return an error during provisioning should still be cleaned
up so that they don't leak any resources they may have allocated before
the error occurred. Cleanup should be able to run even if Provision does
not complete fully.

1 files changed, 3 insertions, 2 deletions

diff --git a/modules.go b/modules.go
index 3ca53841b..2d01eb3b5 100644
--- a/modules.go
+++ b/modules.go
@@ -253,9 +253,10 @@ type Validator interface {
 
 // CleanerUpper is implemented by modules which may have side-effects
 // such as opened files, spawned goroutines, or allocated some sort
-// of non-local state when they were provisioned. This method should
+// of non-stack state when they were provisioned. This method should
 // deallocate/cleanup those resources to prevent memory leaks. Cleanup
-// should be fast and efficient.
+// should be fast and efficient. Cleanup should work even if Provision
+// returns an error, to allow cleaning up from partial provisionings.
 type CleanerUpper interface {
 	Cleanup() error
 }