RFR: 8238566: java.security.Provider$Service.supportsParameter() is racy

[Arthur Eubanks]

Webrev: http://cr.openjdk.java.net/~aeubanks/8238566/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8238566

Found by TSAN, java.security.Provider$Service.supportsParameter() is racy.
We haven't observed any actual bad behavior, but reasoning through it seems
like bad behavior is possible.

http://hg.openjdk.java.net/jdk/jdk/file/62b5bfef8d61/src/java.base/share/classes/java/security/Provider.java#l1927

The synchronized block seems to not have any effect on correctness.

Example race:
T1 in hasKeyAttributes() writes true to hasKeyAttributes and fills out
supportedFormats/supportedClasses.

T2 in hasKeyAttributes() racily reads hasKeyAttributes as true, but then in
supportsKeyFormat() racily reads supportedFormats as null. It can then
improperly return false from supportsParameter().
There is no synchronization between T1 and T2 because T2 never does any
synchronization, so T2 can read what T1 writes in any order.

Fix is to make all of hasKeyAttributes() synchronized.
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