git p4 test: fix badp4dir test

git p4 test: fix badp4dir test

The construct used to get the return code was flawed, in that
errors in the &&-chain before the semicolon were not caught.  Use
the standard test_expect_code instead.

Set PATH in a subshell instead of relying on the bashism of
setting it just for a single command.

And fix the grep line so it doesn't worry about grep segfaults,
and doesn't fail for i18n issues.

Reported-by: Johannes Sixt <redacted>
Signed-off-by: Pete Wyckoff <redacted>
Signed-off-by: Junio C Hamano <redacted>