return a useful error for etcd Lock when aborting the Lock operation instead of nil, nil
return a useful error for etcd Lock when aborting the Lock operation instead of nil, nil

Signed-off-by: Alexandre Beslic <a2bebfa25877ed8f3a644256dc060dfe32006f27@docker.com>

kasisnu/libkv,polyverse-security/libkv,DIREKTSPEED-LTD/libkv,zyclonite/libkv,KimTaehee/libkv,KimTaehee/libkv,DIREKTSPEED-LTD/libkv,polyverse-security/libkv,kasisnu/libkv,zyclonite/libkv