consistent escaping for ovftool uri creds

I got thrown for a loop since the username is uri-escaped but the password was not.

I got thrown for another couple of loops due to the multiple levels of interpretation involved:
* JSON syntax requires backslashes to be slash-escaped. Some vCenter deployments use windows domain-style usernames DOMAIN\user
* the [OVFTOOL docs](https://www.vmware.com/support/developer/ovf/ovf301/ovftool-301-userguide.pdf) specify that "you must escape special characters" when part of the user name or password
* different shell rules in windows cmd.exe, powershell, linux

I'd say escape both or neither. Sublime was nice enough to warn me that \\[:alpha:] isn't valid JSON, but not everyone will be using a validating editor.