Test: add temporary checking in 028.watchdog_enable_consensus_with_half_votes.

Test: add temporary checking in 028.watchdog_enable_consensus_with_half_votes.

We often see a timeout error in the buildfarm test. Analyzing the
buildfarm log shows:

2024-07-10 03:41:31.044: watchdog pid 29119: FATAL:  failed to create watchdog receive socket
2024-07-10 03:41:31.044: watchdog pid 29119: DETAIL:  bind on "TCP:50010" failed with reason: "Address already in use"

I suspect there's something wrong in watchdog shutdown process. To
confirm my theory, add sh command to show all process named "pgpool"
at the end of each test cycle.