Fix props file newline potential bugs

[DomGarguilo]

While doing some testing, I added a property to accumulo.properties via an echo ... >> command, assuming there was a newline at the end of the file. There wasn't, so it appended the property to the value of the final line, which messed things up.

This PR adds a newline to the props file. I also did some digging and found that the encryption plugin relied on that newline too. Its first property was getting tacked onto the end of the last line, so instance.crypto.opts.key.uri never actually got set. I changed that part of the plugin to write its props as a block with a blank line and a comment before it, so it doesn't rely on the newline anymore (even though it is there now).

While I was in there, I also noticed the plugin had the accumulo-core jar version hardcoded to 2.x, so I made that version agnostic.

[ctubbsii]

Your echos in a block with a consolidated file append redirect was good, but I think this heredoc version I added is a little more readable... don't have to deal with quotes as much, and no redundant echo commands.

[DomGarguilo]

Your echos in a block with a consolidated file append redirect was good, but I think this heredoc version I added is a little more readable... don't have to deal with quotes as much, and no redundant echo commands.

Yea your version is better. Thanks for the improvements.