envsetup,product,ninja: enable symlink traversal

When searching device, product, or hardware, allow
find to follow symlinks.

Add KATI_EMULATE_FIND=false to allow disabling the find
emulator which changes findleaves.py behavior wrt
symlinks.

BUG=24605247
TEST=works with CL:783781 (without the find wrapper in that CL)

Change-Id: Ia9d0e4add391a56f34828a09a6cec3f435ccc548