tools/internal/svctool: fix args parsing and output
tools/internal/svctool: fix args parsing and output

There were a couple of bugs lingering:
* running svc tools without args didn't actually work
* usage and printed errors were not properly formatted

TBR=iannucci@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1721713003

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