(maint) Fix up nspooler list active bug

[cthorn42]

If no reason is defined for checking out a nspooler VM we'd get a nil
reference error message when listing active nspooler VMs. This PR fixes
that.

[cthorn42]

The error for reference is:

Traceback (most recent call last):
	10: from /Users/cthorn/repo/vmfloaty/bin/floaty:8:in `<main>'
	 9: from /Users/cthorn/repo/vmfloaty/lib/vmfloaty.rb:583:in `run'
	 8: from /Users/cthorn/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/commander-4.6.0/lib/commander/delegates.rb:18:in `run!'
	 7: from /Users/cthorn/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/commander-4.6.0/lib/commander/runner.rb:58:in `run!'
	 6: from /Users/cthorn/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/commander-4.6.0/lib/commander/runner.rb:444:in `run_active_command'
	 5: from /Users/cthorn/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/commander-4.6.0/lib/commander/command.rb:157:in `run'
	 4: from /Users/cthorn/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/commander-4.6.0/lib/commander/command.rb:187:in `call'
	 3: from /Users/cthorn/repo/vmfloaty/lib/vmfloaty.rb:130:in `block (2 levels) in run'
	 2: from /Users/cthorn/repo/vmfloaty/lib/vmfloaty/utils.rb:113:in `pretty_print_hosts'
	 1: from /Users/cthorn/repo/vmfloaty/lib/vmfloaty/utils.rb:113:in `each'
/Users/cthorn/repo/vmfloaty/lib/vmfloaty/utils.rb:149:in `block in pretty_print_hosts': undefined method `empty?' for nil:NilClass (NoMethodError)

The object in question this was the value I had when looking at it in a pry statement:
{"fqdn"=>"arm64-centos7-2.ops.puppetlabs.net", "os_triple"=>"centos-7-arm64", "user"=>"christopher.thorn", "tags"=>"", "remaining_lifetime"=>5.6}

[sbeaulie]

Thanks for fixing this