RFR: 8224112: [TESTBUG] java/util/Base64/TestEncodingDecodingLength.java should be skipped with insufficient memory

[Jie Fu]

Hi all,

JBS:    https://bugs.openjdk.java.net/browse/JDK-8224112
Webrev: http://cr.openjdk.java.net/~jiefu/8224112/webrev.00/

java/util/Base64/TestEncodingDecodingLength.java may fail due to 
insufficient memory when our test machine is busy.
It might be better to skip it when the available memory is insufficient.
Could you please review it and give me some advice?

Thanks a lot.
Best regards,
Jie