dtc: Remove some small bashisms from test scripts

[Segher Boessenkool]

> Some of the helper scripts used to run testcases contain some
> constructs that are bashisms.  Or at least which don't work on dash,
> the minimal shell used as /bin/sh on recent Ubuntu systems.

Both of these (the >& redirection, and "source" searching the current
directory if the script isn't found in $PATH) are indeed bashisms.

This patch looks good to me.


Segher