MB-20869: Simplify test to fix intermittent test_access_scanner failure

MB-20869: Simplify test to fix intermittent test_access_scanner failure

In test_access_scanner the check that the number of non-resident items
was less than 6% of the total is incorrect - it was using integer
division (6/100) and hence the RHS of the check was always zero, which
would always succeed. Fix the check so it calculates the percentage
correctly.

Additionally we did not wait for the previous AccessScanner run to
finalize - which meant that the second start of the access acanner
could fail to start (and consequently we would timeout with the
message:

    Exceeded maximum wait time of 60000000us waiting for stat
    'ep_num_access_scanner_runs' to be greater or equal than 8 -
    aborting.

To solve this, change to just one iteration of creating the file (not
sure why it did two before), and move the increment of stats.alogRuns
to /after/ the access log files are renamed.

Change-Id: I6c3b6eeed91302fd7fa67dfade6ae954078fc125
Reviewed-on: http://review.couchbase.org/67884
Reviewed-by: Manu Dhundi <manu@couchbase.com>
Tested-by: buildbot <build@couchbase.com>