cmd_test: evaluate to false without any arguments

cmd_test: evaluate to false without any arguments

This emulates bash:
$ if test; then echo yes; else echo no; fi
no

Currently, the code sets expr = -1 in this case, which gets mapped to
0 (true) at the end of do_test() by the logical -> shell exit code
conversion.

Signed-off-by: Stephen Warren <swarren@nvidia.com>