Fix AUFS silent mount errors on many layers

Fixes #1171
Fixes #6465

Data passed to mount(2) is clipped to PAGE_SIZE if its bigger. Previous 
implementation checked if error was returned and then started to append layers 
one by one. But if the PAGE_SIZE clipping appeared in between the paths, in the 
permission sections or in xino definition the call would not error and 
remaining layers would just be skipped(or some other unknown situation).

This also optimizes system calls as it tries to mount as much as possible with 
the first mount.


Signed-off-by: Tõnis Tiigi <tonistiigi@gmail.com> (github: tonistiigi)
Merge pull request #9151 from tonistiigi/aufs-clipping-fix

Fix AUFS silent mount errors on many layers