[Integrated] RFR: Update to Oracle Linux 7.6

[duke]

Changeset: 818fff54
Author:    Erik Helin <ehelin at openjdk.org>
Date:      2019-09-18 08:21:56 +0000
URL:       https://git.openjdk.java.net/skara/commit/818fff54

Update to Oracle Linux 7.6

Reviewed-by: rwestberg

! test.dockerfile