OrangeFS: Change almost all instances of the string PVFS2 to OrangeFS.

OrangeFS was formerly known as PVFS2 and retains the name in many places.

I leave the device /dev/pvfs2-req since this affects userspace.

I leave the filesystem type pvfs2 since this affects userspace. Further
the OrangeFS sysint library reads fstab for an entry of type pvfs2
independently of kernel mounts.

I leave extended attribute keys user.pvfs2 and system.pvfs2 as the
sysint library understands these.

I leave references to userspace binaries still named pvfs2.

I leave the filenames.

Signed-off-by: Yi Liu <yi9@clemson.edu>
[martin@omnibond.com: clairify above constraints and merge]
Signed-off-by: Martin Brandenburg <martin@omnibond.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>