In preparation for subsequent changes.

No functional change.

Bug 11093

We shouldn't umount the NSs until the step FD is closed.

In preparation for next commit as well.

Bug 11093

Now, if umount2 for basepath fails, it still frees everything up.

In preparation for subsequent changes as well.

Bug 11093

No functional change.

This is to match the new naming of the config file better.

Bug 11099

No functionality change.

Bug 11099

Bug 8993.

TOCTOU issue comes from combining stat() with another syscall manipulating
the file afterwards. This removes the unneeded stat() calls in favor of
handling the potential error condition from the successive syscall.

CID 219698, 219701

Bug 8993.

CID 219702.

CID 219702

Coverity CID 219700

The mount command relies on bind mounting and being able to
create private mounts and bind mount namespaces to it.  At the time of
writing this it doesn't work there.

Bug 8993

Bug 8993

Adds a 'tmpfs' job container plugin that moves jobs
into their own namespace consisting of a private /tmp and a
private /dev/shm. The plugin also provides the ability to have
a namespace.conf that sets the basepath for the plugin to
create the bind mounts as well as an initialization script that
can be used to set up the namespace.

Signed-off-by: Aditi Gaur <agaur@lbl.gov>