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Querying the 'fiptool' for help or help <command> should return 0
return status (success) and not 1 (failure). In the other hand, if tool is
executed with any other command (not help) where command's parameters are
either missing or wrong, then the tool should return non-zero (failure). Now,
the 'usage' function caller is the one that passes the return status.

Change-Id: Id5eea91037cd810fb1e34a42e8199ef504f5daa4
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>