Correctly handle '*' in /etc/filesystems

Correctly handle '*' in /etc/filesystems

The /etc/filesystems file can contain a '*' on the last line to
indicate that /proc/filessystems should be tried next. We have
a check that this '*' only occurs on the last line. Unfortunately
when we then start reading /proc/filesystems, we mistakenly think
we've seen '*' in /proc/filesystems and fail

* src/lxc/lxc_container.c: Skip '*' validation when we're reading
  /proc/filesystems