DP: Add log message for get account info Reviewed-by: Petr Čech <pcech@redhat.com>

DP: Remove old data provider interface Reverse data provider interface is moved to a better location in NSS responder. All responders now can have an sbus interface defined per data provider connection. The unused old data provider interface is removed. Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>

PROVIDER: Conversion empty string from D-Bus to NULL This patch fixes the issue with empty string recieving from D-Bus. Data providers obtains NULL. So this is simple conversin. Resolves: https://fedorahosted.org/sssd/ticket/3084 Reviewed-by: Pavel Březina <pbrezina@redhat.com>

DP: rename be_acct_req to dp_id_data Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>

DP: Add function to get be_ctx directly from dp_client Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

DP: Move be_req_acct and remove discard_const Reviewed-by: Sumit Bose <sbose@redhat.com> Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>

DP: Switch to new interface Reviewed-by: Sumit Bose <sbose@redhat.com> Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>