Entity field access condition 2281113b

Updated version of my previous patch;  I've changed branches due to some very bad problems with "git rebase".

I'm aware I have two commits that appear here.  That's the problem -- I can't get git to go lower without pulling in commits I don't own.  If you folks can tell me how to fix this, much thanks.

The patch creates the plugin and test for the issue.
Are you referring to the "$condition = NULL" section?

I am trying to test for plugin discovery.  But it does not currently work as I expected;  having $this->assertNotNull($condition) does not end execution in my tests when $condition is NULL, and execution continues into "$condition->setContext('node..." where it dies.

I can certainly remove that if you don't think it's needed.

If it's for the getUser() section:  when looking for a utility to create a user directly, I did not find EntityUnitTestBase::createUser(), which does appear to do what I need -- just found it now.  But I can easily use that instead.

Related to that:  can I extend the rules_test module to create a field with access control, via a permission?  This would be a lot easier than try to create the access control in the test itself, since all I'll need to do is attach the field, and assign the user to a permission defined in rules_test?

I can make that change as part of this issue, or as a separate issue, however you see appropriate.