libfabric: default 1.8.1 (#15337)

Since 1.9.0 is broken for Darwin, which impacts many developers, and
the fix is still a RC, let's keep the previous release as default.

This avoids distruption for OSX developers and CI.

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

@@ -17,8 +17,8 @@ class Libfabric(AutotoolsPackage):
 
     version('master', branch='master')
     version('1.9.1rc1', sha256='fdf89a0797f0d923aaef2c41cc70be45716e4d07dc5d318365b9c17795eb49ab')
-    version('1.9.0', sha256='559bfb7376c38253c936d0b104591c3394880376d676894895706c4f5f88597c', preferred=True)
-    version('1.8.1', sha256='3c560b997f9eafd89f961dd8e8a29a81aad3e39aee888e3f3822da419047dc88')
+    version('1.9.0', sha256='559bfb7376c38253c936d0b104591c3394880376d676894895706c4f5f88597c')
+    version('1.8.1', sha256='3c560b997f9eafd89f961dd8e8a29a81aad3e39aee888e3f3822da419047dc88', preferred=True)
     version('1.8.0', sha256='c4763383a96af4af52cd81b3b094227f5cf8e91662f861670965994539b7ee37')
     version('1.7.1', sha256='f4e9cc48319763cff4943de96bf527b737c9f1d6ac3088b8b5c75d07bd719569')
     version('1.7.0', sha256='b3dd9cc0fa36fe8c3b9997ba279ec831a905704816c25fe3c4c09fc7eeceaac4')