Fix race in test "CLUSTER SLOT-STATS cpu-usec for blocking commands, unblocked on timeout"

[zuiderkwast]

This fix changes the timeout for BLPOP in this test case from 1 second to 0.5 seconds.

In the test case quoted below, the procedure wait_for_blocked_clients_count waits for one second by default. If BLPOP has 1 second timeout and the first wait_for_blocked_clients_count finishes very fast, then the second wait_for_blocked_clients_count can time out before the BLPOP has been unblocked.

    test "CLUSTER SLOT-STATS cpu-usec for blocking commands, unblocked on timeout." {
        # Blocking command with 1 second timeout.
        set rd [valkey_deferring_client]
        $rd BLPOP $key 1

        # Confirm that the client is blocked, then unblocked after 1 second timeout.
        wait_for_blocked_clients_count 1
        wait_for_blocked_clients_count 0

As seen in the definition of wait_for_blocked_clients_count, the total time to wait is 1 second by default.

proc wait_for_blocked_clients_count {count {maxtries 100} {delay 10} {idx 0}} {
    wait_for_condition $maxtries $delay  {
        [s $idx blocked_clients] == $count
    } else {
        fail "Timeout waiting for blocked clients"
    }
}

Fixes #1121

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.86%. Comparing base (f951a1c) to head (3672303).
Report is 2 commits behind head on unstable.

Additional details and impacted files

@@            Coverage Diff            @@
##           unstable    #1416   +/-   ##
=========================================
  Coverage     70.85%   70.86%           
=========================================
  Files           118      118           
  Lines         63612    63612           
=========================================
+ Hits          45075    45079    +4     
+ Misses        18537    18533    -4     

see 12 files with indirect coverage changes