Add mqtt plugin to subscribe to telemetry data

remove extra case list print out.

add randome insert many records with NULL then commit.

[TD-388] drop dnode in community version

add precalculation interface

td-337: add error log when have to call pthread_cancel

Feature/query

fix TD-394

fix general/insert/insert_drop.sim error

Hotfix/sangshuduo/add case to test insert then import

Feature/2.0tsdb

Hotfix/boundary

create/alter table: only send actual tag data to reduce message size

Feature/pytest output sql command to file

add test cases for filters