etcd PR 11104 (https://github.com/etcd-io/etcd/pull/11104) implemented mutex
TryLock. Since it's only available in etcd master just copy relevant code and
add a TODO to remove it when updating the etcd client to a version implementing
TryLock.
Use TryLock everywhere where it'll be useful.
Just a raw replace of "github.com/pkg/errors".
Next steps will improve errors (like remote errors, api errors, not exist errors
etc...) to leverage its functionalities
Simone Gotti