Fix --dump-cfg argument handling in run-test

This patch fixes a bug which was introduced in
9e73fcdbbdc302d9ed680662b0f86376c8baab10 when converting the run-test
script from bash to Python. The argument's value is now read as the
user-supplied string instead of a constant string literal "{arg}",
resulting in a correctly produced .cfg file.

Test: test-art-host, test-art-target.

Change-Id: I76e550edcfc66c9746e77d767e830412e0cf90cd
1 file changed