this fixes #982 where files with fid >4294967295 were not considered for
garbage collection.

files with fxid coded on 8 or 9 characters in hexadecimal should be considered for GC (8 is not enough).

#881 cta-fst-gcd logs can be now sent to stdout by command line option for container based deployments

An example value of sys.retrieve.error is as follows:

[itctabuild02] ~ > sudo eos attr ls /eos/dev/userfiles/testdir_1/test_1 | grep sys.retrieve.error
sys.retrieve.error="Garbage collected at 2019/09/09 16:27:26.609570"
[itctabuild02] ~ >

cta-fst-gc now logs an error if it cannot list the contents of an FST filesystem or if determine the filesystem's sub directories

ctafstgcd.py no longer logs an ERROR when it fails to stat() a file that has been deleted by the FST