let tftpd-hpa change the uid and gid of the process

tftpd-hpa try to change the uid and gid of the process before serving a file
and it can't if xinetd start the process with a user other than root.

This result to this following message and tftp can't serve file
 in.tftpd[17609]: cannot set groups for user nobody

To customise user/group of the running process we need to use -u option
Update tftp xinetd fix.

* Remove xinetd defaults for user/group.
* Fix spec tests.
Whitespace changes in rspec file.
Merge pull request #18 from nanliu/tb/xinetd

Fix xinetd user/group permission.
Update for 0.2.1 release
Merge pull request #19 from nanliu/tb/release

Update for 0.2.1 release
Require the package on the tftp xinetd service.

The xinetd::service type drops an xinetd config. That config is invalid
before the tftp package is installed and during that window xinetd may
be started. xinetd will start with tftp ignored, and will need to be
manually restarted to enable tftp. This change eliminates that window.
Merge pull request #20 from benburkert/master

Require the package on the tftp xinetd service.