lorax-composer: Update the yum metadata at startup

Otherwise it can become out of date and depsolving will fail.

src/pylorax/api/yumbase.py

@@ -22,7 +22,6 @@ log = logging.getLogger("lorax-composer")
 import ConfigParser
 from fnmatch import fnmatchcase
 from glob import glob
-from distutils.util import strtobool
 import os
 import yum
 # This is a hack to short circuit yum's internal logging
@@ -102,4 +101,13 @@ def get_base_object(conf):
         if any(map(lambda pattern: fnmatchcase(name, pattern), enabled_repos)):     # pylint: disable=cell-var-from-loop
             yb.getReposFromConfigFile(repo_file)
 
+    # Update the metadata from the enabled repos to speed up later operations
+    log.info("Updating yum repository metadata")
+    for r in yb.repos.sort():
+        r.metadata_expire = 0
+        r.mdpolicy = "group:all"
+    yb.doRepoSetup()
+    yb.repos.doSetup()
+    yb.repos.populateSack(mdtype='all', cacheonly=1)
+
     return yb