Connhelpers do not register automatically

Without explicitly importing the connhelpers (by way of import _ "path" or a real import), they are not registered. This causes clients using connhelper handled daemon URLs to throw nondescript errors.

Errors are similar to: connection error: desc = "transport: error while dialing: dial docker-container: unknown network docker-container"

As far as I can tell, for users utilizing the client libraries on their own, importing the file in one location should resolve the issue as it triggers the init() function. You can also explicitly generate a helper and pass it as an option to the client object, but that is overkill.

Start by tracing connhelper registration and the init() behavior described in the issue, then inspect how client libraries resolve daemon URLs and accept explicit helper options. Reproduce the unknown-network error without an explicit connhelper import; done means supported connhelpers register automatically and the client no longer requires a redundant import or manually supplied helper.