When -mem-prealloc is passed on the command-line, the expected
behavior is to exit if the hugepage allocation fails.  However,
this behavior is broken since commit cc57501d which made
hugepage allocation fall back to regular ram in case of faliure.

This commit restores the expected behavior for -mem-prealloc.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Message-Id: <20160122091501.75bbd42a@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>