RFR(S) : 8180397 : remove jdk.testlibrary.IOUtils

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8180397/webrev.00/index.html
> 92 lines changed: 0 ins; 81 del; 11 mod; 

Hi all,

could you please review this small clean-up which removes jdk.testlibrary.IOUtils class from test library?
IOUtils provides one method readFully(InputStream), which can be replaced by InputStream::readAllBytes() introduced in JDK 9.

this fix is a part of ongoing effort on merging and cleaning up our test libraries[1].

webrev: http://cr.openjdk.java.net/~iignatyev//8180397/webrev.00/index.html
JBS: https://bugs.openjdk.java.net/browse/JDK-8180397
testing: affected tests

[1]  https://bugs.openjdk.java.net/browse/JDK-8075327

Thanks,
-- Igor