* [Fix](Variant) forbit table with variant type doing segment compaction temporarily
TODO fix this corretly in later works
* [Bug](Variant) use lower case name for variant's root, since backend treat parent column as lower case
This PR address the problem as blow:
```
errCode = 2, detailMessage = (172.16.56.137)[CANCELLED]failed to initialize storage reader. tablet=17136, res=[INTERNAL_ERROR]Not found field_name, field_name:Tags.tag_key1, schema:[Thread(8), Tags(9), Source(5), tags.tag_key1(-1), Title(6), Level(3), Time(2), CreateDate(1), Message(7), IP(4), AppId(0)]
```