[8u] RFR 8183349: Better cleanup for jdk/test/javax/imageio/plugins/shared/CanWriteSequence.java and WriteAfterAbort.java

[Zhengyu Gu]

Please review this backport for parity with Oracle 8u271.

The original patch does not apply cleanly. The conflicts are minor, as 
8u version of CanWriteSequence.test() method format is slightly off.

Original bug:  https://bugs.openjdk.java.net/browse/JDK-8183349
Original patch: http://hg.openjdk.java.net/jdk10/jdk10/jdk/rev/93b7bd25273e

8u weberv: http://cr.openjdk.java.net/~zgu/JDK-8183349-8u/webrev.00/

Test:
   Passed both tests on Linux x86_64


Thanks,

-Zhengyu