Add LSF dependency for OpenMPI (#11532)

* Add LSF package, which cannot be installed by Spack and must be
  system-installed. The package install will fail if no external
  LSF is registered in packages.yaml (LSF may not be installed in a
  well-known location and the external entry helps Spack locate it
  for dependents).
* Add LSF dependency to OpenMPI when schedulers=lsf is chosen

var/spack/repos/builtin/packages/lsf/package.py

@@ -0,0 +1,25 @@
+# Copyright 2013-2019 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+
+from spack import *
+
+
+class Lsf(Package):
+    """IBM Platform LSF is a batch scheduler for HPC environments"""
+
+    homepage = "https://www.ibm.com/marketplace/hpc-workload-management"
+    url = "https://www.ibm.com/marketplace/hpc-workload-management"
+
+    # LSF needs to be added as an external package to SPACK. For this, the
+    # config file packages.yaml needs to be adjusted:
+    #   lsf:
+    #     version: [10.1]
+    #     paths:
+    #       lsf@10.1: /usr/local/lsf/10.1 (path to your LSF installation)
+    #     buildable: False
+
+    def install(self, spec, prefix):
+        raise InstallError('LSF is not installable; it is vendor supplied')

var/spack/repos/builtin/packages/openmpi/package.py

@@ -259,6 +259,7 @@ class Openmpi(AutotoolsPackage):
     depends_on('ucx', when='fabrics=ucx')
     depends_on('libfabric', when='fabrics=libfabric')
     depends_on('slurm', when='schedulers=slurm')
+    depends_on('lsf', when='schedulers=lsf')
     depends_on('binutils+libiberty', when='fabrics=mxm')
 
     conflicts('+cuda', when='@:1.6')  # CUDA support was added in 1.7