[asan] Fix size/alignment issues with non-default shadow scale

Fix a couple places where the minimum alignment/size should be a
function of the shadow granularity:
- alignment of AllGlobals
- the minimum left redzone size on the stack

Added a test to verify that the metadata_array is properly aligned
for shadow scale of 5, to be enabled when we add build support
for testing shadow scale of 5.

Differential Revision: https://reviews.llvm.org/D39470

llvm-svn: 318395