userboot: support environment and symlinks in test application

[stevek]

Summary

Pass the environment on to the loader.
Also define USERBOOT=1 in the environment varables.

Add support for symlinks in the test application open callback.

stat the root directory when opening file
Without this, running "ls" command on the root directory encounters
issues getting the directory listing.

Obtained from: Juniper Networks, Inc.

[jhb]

stand/userboot/test/test.c

112

Do you still want this case? I think in the new code open() will fail with EFAULT due to the NULL path pointer, but ENOENT does seem like it might be the better error code if there is no host base path.

525

[stevek]

stand/userboot/test/test.c

112

That case is in the test_open() function.

[stevek]

Added parenthesis based on comments.