[master] Merge branch 'trac2592' (getLease4 in memfile LeaseMgr)
Conflicts: ChangeLog src/lib/dhcpsrv/memfile_lease_mgr.cc src/lib/dhcpsrv/memfile_lease_mgr.h src/lib/dhcpsrv/tests/mysql_lease_mgr_unittest.cc
Conflicts: ChangeLog src/lib/dhcpsrv/memfile_lease_mgr.cc src/lib/dhcpsrv/memfile_lease_mgr.h src/lib/dhcpsrv/tests/mysql_lease_mgr_unittest.cc