Do not use recursive symlinks in "git lb-clone-pkg"

From a discussion on lhcb-distributed-analysis:

Checking input sandbox for this job You still submit jobs with links to current directory

CastelaoDev_v1r2/WG/PIDCalib:
total 17
-rw-r--r--. 1 [...]  983 Nov 15 22:37 CMakeLists.txt
drwxr-xr-x. 2 [...] 2048 Nov 15 23:20 cmt
drwxr-xr-x. 2 [...] 2048 Nov 15 22:37 doc
drwxr-xr-x. 2 [...] 4096 Feb  7 19:30 scriptsR2
drwxr-xr-x. 2 [...] 2048 Nov 15 22:38 sTables
lrwxr-xr-x. 1 [...]    1 Feb 12 16:51 v6r999 -> .
lrwxr-xr-x. 1 [...]    1 Feb 12 16:51 v999r999 -> .
lrwxr-xr-x. 1 [...]   16 Feb 12 16:51 WG_PIDCalibEnvironment.xml -> WG_PIDCalib.xenv
-rw-r--r--. 1 [...]  238 Nov 15 22:37 WG_PIDCalib.xenv
drwxr-xr-x. 2 [...] 2048 Feb  7 19:34 x86_64-slc6-gcc62-opt

[...] It is impossible to get output sandbox for them.

[...] as pilots executing your jobs looping infinitely at these directories.