fix for flaky psync2 test
fix for flaky psync2 test

*** [err]: PSYNC2: total sum of full synchronizations is exactly 4 in tests/integration/psync2.tcl
Expected 5 == 4 (context: type eval line 6 cmd {assert {$sum == 4}} proc ::test)

issue was that sometime the test got an unexpected full sync since it
tried to switch to the replica before it was in sync with it's master.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis