Updated omnibus postinst script to symlink to appbundle created binstubs

[miah]

The binstubs created by rubygems, and linked to by our omnibus postinst script error when they encounter GEM_HOME or GEM_PATH set to anything outside of the /opt/inspec/embedded directory.

On my laptop with chruby the environment variables GEM_HOME and GEM_PATH are set when I create a new shell. When I invoke InSpec via /usr/local/bin/inspec or /opt/inspec/embedded/bin/inspec I get the following error:

$ /usr/local/bin/inspec version
/opt/inspec/embedded/lib/ruby/2.4.0/rubygems.rb:271:in `find_spec_for_exe': can't find gem inspec (>= 0.a) (Gem::GemNotFoundException)
	from /opt/inspec/embedded/lib/ruby/2.4.0/rubygems.rb:299:in `activate_bin_path'
	from /usr/local/bin/inspec:23:in `<main>'

This error persists until I unset GEM_HOME and unset GEM_PATH.

$ unset GEM_PATH GEM_HOME
$ /usr/local/bin/inspec version
2.0.16

The inspec binstub created by appbundler correctly deals with GEM_HOME and GEM_PATH.

$ /opt/inspec/bin/inspec version
2.0.16

Because our omnibus package already uses appbundler, the fix is to change our symlink to use it rather than the rubygems binstub.

This problem exists in older 1.x packaged releases as well.

Fixes #2727

[adamleff]

This looks like a fine change, and matches what we do in other projects (see https://github.com/chef/chef/blob/master/omnibus/package-scripts/chef/postinst#L14 for example).

For consistency with other projects, I'd like to see the var name stay the same. Also, before we approve and proceed, have we done an ad-hoc Jenkins build from this branch and tested the resulting package on macOS and one other OS (such as Ubuntu) just to make sure this succeeds?

Another thing to think about (outside of this PR) is a change to the Jenkins "test" job to do a GEM_HOME=/nonexistent/path GEM_PATH=/nonexistent/path /usr/local/bin/inspec version or whatever the symlink path is to ensure the package works properly.

[adamleff]

To keep this consistent with other omnibus projects, I would leave this as INSTALLER_DIR and just change the value to /opt/inspec

[miah]

Thanks for the feedback @adamleff =)

[miah]

Excellent comment about Jenkins test as well, I'll add one!

[miah]

I added two scripts to this PR which will be called by Jenkins during the verify stage.

[jerryaldrichiii]

Looks good to me. Great work @miah!

[miah]

@adamleff What do you think friend? =)

[adamleff]

I dig it!

Because he digs it! 🕳

[jquick]

Thanks @miah !