Typo "possibilites" should be "possibilities"

Misspelling of "possibilities" found in
class QueryAlarmHistoryController in
/ceilometer/ceilometer/api/controllers/v2.py

Change-Id: I88a6b3f56198c254763d324f1e4df5302f8d1094
Merge "Typo "possibilites" should be "possibilities""