(i.e. delete paths from CTADIRSFAILED)

There are now 3 possible sources for directories:
- (default) CTADIRSHELPER
- --delta   CTADELTADIRSHELPER
- --retry   CTADIRSFAILED

Processing of directories no longer halts on an error: all directories
will be attempted and failures will be saved (with EOS error message) for
offline analysis and retry.

This table will keep a list of directory imports which failed.
eos-import-dirs now has a --retry option so they can be retried.

Now we are also tolerant of whether paths in config file do or do
not have a trailing slash.

Pathnames from the DB must have a leading slash if we have to strip off
the CASTOR prefix, but in any case we will convert all filenames to
absolute filenames by adding the EOS prefix.

This test is failing, probably because EOS version in CI was compiled
against an incompatible version of the grpc protobuf. Will obtain a new
EOS version and retry.

These protobuf fields are intended only for retrieiving file/container
metadata and are ignored when injecting.