[BUILD] Close stale Pull Requests.

Closes #11610
Closes #15411
Closes #15501
Closes #12613
Closes #12518
Closes #12026
Closes #15524
Closes #12693
Closes #12358
Closes #15588
Closes #15635
Closes #15678
Closes #14699
Closes #9008

Author: Sean Owen <sowen@cloudera.com>

Closes #15685 from srowen/CloseStalePRs.