Fix mdp Makefile and properly open keyring file

1. Fix the mdp Makefile: It is called libservald.so,
not libserval.so

2. Properly open the keyring file: Must call keyring_
enter_pin(file, ""); to get access to the default
identities.
Merge pull request #6 from hawkinswnaf/release-0.6.5.4

Fix mdp Makefile and properly open keyring file