Add ?IMPLIES(length(Ops) > 1, ...) to avoid legit model ambiguity
in cases where the op list is too short to make a reasonable &
correct guess of behavior.

Use eqc:testing_time/2 for test length & EUnit timeout at 2x
testing time.
Don't always return 'true', and re-indent the catch clause
Merge branch 'slf-bitcask_qc_expiry-intermittent-failures'