[FLINK-21853][e2e] Harden common_ha.sh#ha_tm_watchdog
[FLINK-21853][e2e] Harden common_ha.sh#ha_tm_watchdog

This commit hardens the common_ha.sh#ha_tm_watchdog function by always starting
the expected number of TaskManagers. This will ensure that the e2e tests that are
using this function also pass if a TaskManager dies accidentally.

apache/flink,lincoln-lil/flink,StephanEwen/incubator-flink,gyfora/flink,zentol/flink,zentol/flink,zentol/flink,apache/flink,godfreyhe/flink,godfreyhe/flink,lincoln-lil/flink,tony810430/flink,zjureel/flink,tony810430/flink,zjureel/flink,godfreyhe/flink,godfreyhe/flink,xccui/flink,twalthr/flink,zjureel/flink,twalthr/flink,zjureel/flink,tony810430/flink,apache/flink,lincoln-lil/flink,wwjiang007/flink,xccui/flink,apache/flink,wwjiang007/flink,wwjiang007/flink,wwjiang007/flink,twalthr/flink,StephanEwen/incubator-flink,zentol/flink,zjureel/flink,xccui/flink,zentol/flink,tony810430/flink,apache/flink,zentol/flink,apache/flink,godfreyhe/flink,wwjiang007/flink,gyfora/flink,twalthr/flink,lincoln-lil/flink,StephanEwen/incubator-flink,twalthr/flink,godfreyhe/flink,gyfora/flink,wwjiang007/flink,wwjiang007/flink,zjureel/flink,tony810430/flink,gyfora/flink,apache/flink,tony810430/flink,tony810430/flink,twalthr/flink,xccui/flink,StephanEwen/incubator-flink,zentol/flink,godfreyhe/flink,gyfora/flink,StephanEwen/incubator-flink,lincoln-lil/flink,gyfora/flink,zjureel/flink,xccui/flink,gyfora/flink,lincoln-lil/flink,StephanEwen/incubator-flink,lincoln-lil/flink,xccui/flink,twalthr/flink,xccui/flink