when set dim A to mandatory，can't find cuboid only contain dim A

[Johnson]

hi，all：
I found a problem，when set dim A to mandatory，can't find cuboid only contain 
dim A，example：
dim：A，B，C  ； mandatory：A  ；rowkey order A B C
when build success，exists cube combination：AB(110),AC(101),ABC(111)，why A(100) 
not exists？
I looked at the source code，found this configuration：


I set kylin.cube.aggrgroup.is-mandatory-only-valid：true,rebuild cube，it doesnt 
work，cube combination A(100) still not exists。


ENV：
kylin version ：2.6.2
build engine：spark
kylin.cube.cubeplanner.enabled：false
kylin.cube.aggrgroup.is-mandatory-only-valid：true