mem: fix hugepage mapping error messages

mem: fix hugepage mapping error messages

Running secondary is tricky due to the need to map the memory region
at the right place in VM, which is whatever primary has chosen. If the
base address for primary happens to by already mapped in the
secondary, we will hit precisely these error messages (depending if we
fail on the config region or the hugepages). This is why there is
already a comment about ASLR.

The issue is that in most cases, remapping does not happen and "errno"
is not changed and therefore stale. In our case, we got a "permission
denied", which sent us down the wrong track. It's such a common error
for secondary that I feel this error message should be unambiguous and
helpful.
The call to close was also moved because close() may override errno.

Signed-off-by: Jean Tourrilhes <jt@labs.hpe.com>