Don't use $PPID

If17221a74b081ebfec8dbf7076b2cd702861eda9 stopped reading $PPID
for the !$TMPDIR case, but still reads $PPID if $TMPDIR is set.
Always use $CWD and $USER to determine the test directory.

Bug: 71766439
Test: m TMPDIR=/tmp nothing && m TMPDIR=/tmp nothing
Change-Id: Iafc5e27328afc32ccaf2b9daf4b5d0bc597bebc5
1 file changed