quilt: run ptest as normal user

quilt: run ptest as normal user

When the user is root, run quilt ptest, the faildiff.test failed.
Because in the faildiff.test, we drop the read permission of the
file test.txt, we can't "quilt refresh" as normal user, so we got
the following:
	>~ .*diff:test\.txt: Permission denied
	> Diff failed on file 'test.txt', aborting
But when the user is root, we can access the file, so we got the
following:
	> Nothing in patch patchs/test.diff
So the faildiff.test was failed. We should create a normal user
to run the ptest in the run-ptest scripts to slove the problem.

Signed-off-by: Dengke Du <dengke.du@windriver.com>