Parallelize processing of jar files for ClasspathDeviceInfo.

The test involves downloading all jar files and using dex2lib on each
to get a list of class names for further reporting.

Instead of doing all the work sequentially, parallelize where possible.

Runtime on my workstation with a cuttlefish device is at least twice
faster now.

Bug: 187659463
Test: atest CtsEdiHostTestCases:android.edi.cts.ClasspathDeviceInfo#testCollectDeviceInfo
Change-Id: Id1698710b65fd694b5862aa035fe1ad5f23cc3f2
Merged-In: Id1698710b65fd694b5862aa035fe1ad5f23cc3f2
(cherry picked from commit 29269413346362f1c6c4d40a3f3a9d5d65ff235e)