RFR 8221172: SunEC specific test is not limited to SunEC

[Adam Petcher]

The regression test I added for JDK-8147502[1] has a minor bug. The test 
only works for SunEC, so the calls to getInstance should specify SunEC 
as the provider. Please review the fix for this test bug---it should 
only take a moment.

Webrev: http://cr.openjdk.java.net/~apetcher/8221172/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8221172

[1] https://bugs.openjdk.java.net/browse/JDK-8147502