RFR: 9: 8156671: Refactor sun/security/rsa/SignatureTest.java

[Rajan Halade]

Please provide your review of patch to refactor SignatureTest. This test 
now runs all signature algorithms with key generated once resulting in 
saving 75% of execution time.

Bug: https://bugs.openjdk.java.net/browse/JDK-8156671
Webrev: http://cr.openjdk.java.net/~rhalade/8156671/webrev.00/
Thanks,
Rajan