RFR: 8255959: Timeouts in VectorConversion tests

[Martin Doerr]

We observed many timeouts in the following test/jdk/jdk/incubator/vector tests:
Vector128ConversionTests.java
Vector256ConversionTests.java
Vector512ConversionTests.java
Vector64ConversionTests.java
VectorMaxConversionTests.java
Some machines don't support vector instructions or fewer of them and C2 uses slower alternatives.

Maybe there are options to make the tests faster, but I just propose to use a larger timeout value for now.

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Commit messages:
 - 8255959: Timeouts in VectorConversion tests

Changes: https://git.openjdk.java.net/jdk/pull/1079/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1079&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255959
  Stats: 5 lines in 5 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1079.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1079/head:pull/1079

PR: https://git.openjdk.java.net/jdk/pull/1079