Revert "testrunner.py: Use list to store command line args"

This reverts commit 534fb7ac092210c9b0c4927a924c330979e3fd4b.

Reason for revert: Speculative revert for failures on git_master-art-host. There are failures like:
-Xusejit:true and -Xint cannot be specified together

The log is also huge and from what I can see the test commands are large with the same options repeated a lot of times. An example failure: https://android-build.corp.google.com/build-details/10277194/targets/art-test

Here's an example of the log that isn't too big to open:
https://android-build.corp.google.com/build-details/10277046/targets/art-optimizing-gcstress-gcverify

Change-Id: Icd5ffe31d8659df81317acce0087b7097d678af1
1 file changed