The Elastic Secrets vault is served via HTTPS with a Let's Encrypt
certificate. The root certificate that cross-signed the Let's Encrypt
certificates were not trusted by the JDK until 8u101. This commit adds a
version check at the start of the build to make it clear the cause of
the underlying issue, and what the fix is.
Relates elastic/x-pack-elasticsearch#541
Original commit: elastic/x-pack-elasticsearch@6bf8076cb6