[8u] RFR 8277224: sun.security.pkcs.PKCS9Attributes.toString() throws NPE

[Zhengyu Gu]

I would like to backport this patch to openjdk8u for parity with Oracle 
8u331.

Bug: https://bugs.openjdk.java.net/browse/JDK-8277224
Patch: 
https://github.com/openjdk/jdk/commit/6bb04626af6574ef1e8d4b7dad0389d4b59f5d08

The original patch does not apply cleanly to 8u. The only conflict is 
the change in PKCS9Attributes.toString() method, where 8u uses 
"StringBuffer buf", while 18 uses "StringBuffer sb" to build string.

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8277224-8u/webrev.00/

Test:
   NonStandardNames.java passed.


Thanks,

-Zhengyu