Extend the replds-instance-create script to set a custom data group

The data directory will be owned by this group, and the
instance-specific user will be a member of the group.
4 jobs for master in 1 minute and 30 seconds
Status Job ID Name Coverage
  Build Pkgsrc
passed #12455
build_pkgsrc:stretch

00:00:17

 
  Build Pkg
passed #12456
amd64
build_pkg:stretch:amd64

00:00:54

passed #12457
arm64
build_pkg:stretch:arm64

00:00:15

 
  Upload Pkg
passed #12458
upload_pkg

00:00:17