RFR (S): 8072687: Update OutputAnalyzer to work with files

[denis kononenko]

Hi All,

Could you please review a small change of OutputAnalyzer class from 
testlibrary.

Webrev link: 
http://cr.openjdk.java.net/~dfazunen/dkononen/8072687/webrev.00/
Bug id: https://bugs.openjdk.java.net/browse/JDK-8072687
Testing: automated
Description:

The purpose of this change is to extend the functionality of 
OutputAnalyzer by adding ability to read output from a file. Sometimes 
we have to analyze output written to a file (test data, logs, etc.). In 
that case we have to read it as a string and pass it into 
OutputAnalyzer's constructor (it could be done in several different 
ways). It would be very convenient to put this code directly into 
OutputAnalyzer. This would allow to make further tests code more cleaner 
and less error prone.

The change consist of two parts:
1) The change: OutputAnalyzer.java, added a new constructor that accepts 
File;
2) The tests: FileOutputAnalyzerTests.java, very basic tests on reading 
functionality.

Thank you,
Denis.