varnish:6 security, bug fix, and enhancement update

varnish 6.0.6-2 - new version 6.0.6 - Resolves: 1795673 - RFE: rebase varnish:6 to latest 6.0.x LTS - Resolves: 1790907 - CVE-2019-20637 varnish: not clearing pointer between two client requests leads to information disclosure - Resolves: 1763958 - CVE-2019-15892 varnish:6/varnish: denial of...