Faster bugreports (3/n)

Post 'DumpHals', 'DumpBoard' and 'DumpIncidentReport' to the
thread pool. 30% is improved compared with single thread run.

Bug: 136262402
Test: atest dumpstate_test
Test: atest dumpstate_smoke_test
Test: atest BugreportManagerTestCases
Test: atest CtsBugreportTestCases
Test: Manual enable and disable parallel run
Test: Manual trigger report using hardware key and shortcut
Change-Id: Iea3a6e676f05149a3f2cfc1fcd475c70ea253d08