virtinst: fix some comment typos

s/occurence/occurrence

Signed-off-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>

virtinst/cli.py

@@ -985,7 +985,7 @@ class VirtCLIParser(object):
 
         if editting and optlist:
             # If an object is passed in, we are updating it in place, and
-            # only use the last command line occurence, eg. from virt-xml
+            # only use the last command line occurrence, eg. from virt-xml
             optlist = [optlist[-1]]
 
         ret = []

virtinst/urlfetcher.py

@@ -665,7 +665,7 @@ class FedoraDistro(RedHatDistro):
         ret = None
         for osinfo in osdict.list_os(typename="linux"):
             if osinfo.name.startswith("fedora") and "unknown" not in osinfo.name:
-                # First fedora* occurence should be the newest
+                # First fedora* occurrence should be the newest
                 ret = osinfo.name
                 break