java8 image appears to fail to download the ftbinstaller

[itzg]

Another problem with the java8 image it appears to fail to download the ftbinstaller and just skips to try deploying it which then fails.

[init] Running as uid=1000 gid=1000 with /data as 'drwxrwsrwx 1 0 2000 42 Mar 21 23:33 /data'
[init] Resolved version given LATEST into 1.18.2 and major version 1.18
[init] Resolving type given FTBA
[init] Installing modpack ID 80, version ID 2112
/start-deployFTBA: line 47: /data/ftb-installer: No such file or directory

Originally posted by @evilhamsterman in #1376 (comment)