Merge pull request prometheus#3952 from prometheus/cut221

*: cut 2.2.1

Merge pull request prometheus#3931 from prometheus/cut200

*: cut v2.2.0

Merge pull request prometheus#3874 from prometheus/22rc1

*: cut 2.2.0-rc.1

Merge pull request prometheus#3352 from prometheus/rc2

Cut v2.0.0-rc.2