pvfs2-client-core hang if restarted without server connectivity

[carns]

David Metheny reported this scenario:

- network connectivity lost on client - pvfs2-client-core restarted (due to a segfault) - pvfs2-client-core attempted "remount" - remount failed - network connectivity restored on client

At this point no operations worked on the PVFS mount point (including unmount). It sounds like the pvfs2-client-core attempted a remount once and then gave up, and subsequent operations just queued up behind it.

We need to at least allow an unmount in this case, or possibly be smarter about retrying the remount if operations continue to come in later.