Clear file_lists caches on master start

The caches do expire quickly (30 sec by default), but if you make a
config change, then quickly restart the master, the caches will still be
younger than the expiry deadline. This commit clears all file lists
caches on master start to ensure that they are properly generated in the
first loop interval.
Strip trailing path separators from gitfs_root
Merge pull request #13257 from terminalmage/issue13185

A couple of gitfs fixes