vmem: vmem_pool_create_in_region() address alignment up to Pagesize

-Update page protection in vmem_pool_create_in_region()
-Update man page
-Update Unit Tests.
For unit tests, we use the macros in unittest.h to avoid uninteresting boiler-plate code that checks results on things we're not testing.  For this case (and the other similar cases you changed), replace the open, if, mmap, if, close, if with a single statement:

```
mem_pool = MMAP(NULL, VMEM_MIN_POOL, PROT_READ|PROT_WRITE,
                                 MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
```