This adds the option `resolvConf` to the host-local IPAM configuration.
If specified, the plugin will try to parse the file as a resolv.conf(5)
type file and return it in the DNS response.
It doesn't seem like container IDs should really have whitespace or
newlines in them. As a complete edge-case, manipulating the host-local
store's IP reservations with 'echo' puts a newline at the end, which
caused matching to fail in ReleaseByID(). Don't ask...
Add an e2e host-local plugin testcase, which requires being able
to pass the datadir into the plugin so we can erase it later.
We're not always guaranteed to have access to the default data
dir location, plus it should probably be configurable anyway.
