libchrome: Don't use the Bionic gtest runner.

libchrome's unit tests are not thread safe and should not be run in
parallel.
Instead of using the Bionic parallel unit tests runner, use a simpler
gtest runner, inpired by the one used by libbrillo.

Bug: 25973681
Change-Id: Ibb06e84524454913a77033c4acc7206138ba16a1
Test: unit tests.