RFR: JDK-8294840: langtools OptionalDependencyTest.java use File.pathSeparator

[Matthias Baesken]

The test/langtools/tools/jdeps/optionalDependency/OptionalDependencyTest.java:
introduced with 8293701 needs to use File.pathSeparator instead of ":" to work on all platforms.

-------------

Commit messages:
 - use File.pathSeparator in OptionalDependencyTest

Changes: https://git.openjdk.org/jdk/pull/10572/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10572&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294840
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10572.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10572/head:pull/10572

PR: https://git.openjdk.org/jdk/pull/10572