@Override
  public void setMasterKeyService(MasterKeyService masterKeyService) {
    this.masterKeyService = masterKeyService;
  }
Tests this CredentialStore for the existence of a credential with the specified alias
<p/>
This implementation is thread-safe, allowing one thread at a time to access the credential store.

@param alias a string declaring the alias (or name) of the credential
@return true if the alias exists; otherwise false
@throws AmbariException if an error occurs while searching forthe credential
ambari-server/src/main/java/org/apache/ambari/server/security/encryption/AbstractCredentialStore.java