Ensure that ntp version is captured

On CentOS 7 `ntpd --version` is outputting:
```
ntpd 4.2.6p5

exit 0
```

However, the first line, with the version number is being outputted to STDERR and thus wasn't being captured.  This caused the Regexp.last_match to be empty which of course failed the cookbook.  This ensures everything is captured.
Catch the error returned from `shell_out!`

Adding the output redirect has changed the nature of the `shell_out`
execution. We need to catch the exception raised by the `shell_out!` method
in order to proceed if there is an error.
Switch to argument-based accessor for `last_match`

When calling `last_match` and not passing an index to the method, it
returns all of the matchers. This was being used to access the matcher
based on the index array. However, if there is a problem and last_match
returns `nil`, then the array accessor raises an error. Passing an
argument to `last_match` returns nil if no result is present at that
position.
Merge pull request #1 from joerocklin/centos7-fix

Updates to Centos7 fix
Merge pull request #58 from jrust/centos7-fix

Ensure that ntp version is captured