Fix "adb push /sdcard/filename"

Don't assume that calling chown(filename, getuid(), getgid())
will always succeed. In the case of /sdcard, a file you create
will be owned by root, so the chown call will fail.

Instead, use uid=gid=-1 so that the chown call is truly a no-op.

Ignore the results of calling chmod. Again, for /sdcard, the
chmod call will never succeed, because the file isn't owned by
the shell user.

Bug: 12441485
Change-Id: I11eaf1d6f6049c1158afc29754fbb7af2baf2c78