Generate 5.2.x BWC indices with the 5.2 script

In #22716 we significantly increased the variety of boolean
representations that are created by the BWC script. The script and the
related tests have only been backported to Elasticsearch 5.3 though.
Hence, if we generate an index with a great variety of boolean
representation but `RestoreBackwardsCompatIT#testOldSnapshot()` tests
only one representation it has to fail.

With this commit we regenerate the BWC indices for 5.2.0 and 5.2.1 with
the older version of the script (which is present on the 5.2 branch) and
only generates one representation of boolean fields as expected by the
test.

Author: danielmitterdorfer