Support for `lb-run --platform best ...`

Automatically map the special platform name best to the best platform supported by the current host.

Requires !147 (merged) to work

LbConfiguration/python/LbConfiguration/SP2/lookup.py

@@ -20,6 +20,7 @@ import logging
 from LbConfiguration.SP2 import path, Error
 from LbConfiguration.SP2.version import (DEFAULT_VERSION, versionKey as _vkey,
                                          LCGInfoName)
+from LbConfiguration.Platform import platform_sort_key
 
 log = logging.getLogger(__name__)
 
@@ -258,7 +259,7 @@ def listPlatforms(name, version, allow_empty_version=False, quiet=False):
     if not platforms:
         (log.debug if quiet else log.warning)(
             'could not find %s/%s in %r', name, version, path)
-    return sorted(platforms)
+    return sorted(platforms, key=platform_sort_key)
 
 
 def findDataPackage(name, version):
@@ -491,7 +492,7 @@ def listROOTPlatforms(version):
                 if l[0].strip().upper() == 'ROOT' and l[2].strip() == version:
                     platforms.add(platform)
                     break
-    return sorted(platforms)
+    return sorted(platforms, key=platform_sort_key)
 
 
 def findLCGForROOT(version, platform):