CONFIG: improve robustness/flexibility for MPI config handling

- use orte-info to determine prefix/libdir for openmpi.
  This removes a run-time dependency on mpicc, which is actually
  only needed for building with MPI (not running with MPI).
  The corresponding openmpi devel package (deb/rpm) will not
  necessarily be installed on a particular system.

- retain mpicc logic if the new logic using orte-info does not
  deliver an answer. Final fallback to using 'orterun' to
  infer prefix/libdir.

- Additional logic for intel and msmpi to make it easier to
  locate these vendor packages within ThirdParty
  (ie, under ThirdParty/opt/...)

CONFIG: improve robustness

- add check for absolute path when adding PATH/LD_LIBRARY_PATH etc.

- prefix more variables with '_foam*' to prevent accidental overwrite
  of userspace shell variables when sourcing

etc/config.csh/complete-wrapper

@@ -9,8 +9,7 @@
 #     Copyright (C) 2017 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
-#     This file is part of OpenFOAM, licensed under GNU General Public License
-#     <http://www.gnu.org/licenses/>.
+#     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
 #
 # File
 #     etc/config.csh/complete-wrapper
@@ -38,14 +37,14 @@ then
 fi
 
 # Preload completion cache
-if [ -f $WM_PROJECT_DIR/etc/config.sh/completion_cache ]
-then  . $WM_PROJECT_DIR/etc/config.sh/completion_cache
+if [ -f "$WM_PROJECT_DIR"/etc/config.sh/completion_cache ]
+then  . "$WM_PROJECT_DIR"/etc/config.sh/completion_cache
 fi
 
 # Use the bash completion function, but retain cache etc.
 _of_complete_tcsh=true
-if [ -f $WM_PROJECT_DIR/etc/config.sh/bash_completion ]
-then  . $WM_PROJECT_DIR/etc/config.sh/bash_completion
+if [ -f "$WM_PROJECT_DIR"/etc/config.sh/bash_completion ]
+then  . "$WM_PROJECT_DIR"/etc/config.sh/bash_completion
 else
     # Could warn about missing file, or treat silently
     echo