Make sure to explicly report VOMS-less proxies

[belforte]

when testing on lxplus, a proxy w/o voms extension was causing

belforte@lxplus738/TC3> crab submit 
Will use CRAB configuration file crabConfig.py
Error executing voms-proxy-info --actimeleft --timeleft --file /tmp/x509up_u8516:
43184

No VOMS attributes found!

Log file is /afs/cern.ch/work/b/belforte/CRAB3/TC3/crab_20211209_165956/crab.log
belforte@lxplus738/TC3> 

which I considered sufficient info for the user. But on sites with a different version of voms-proxy-info (FNALLPC e.g.) the message is the very cryptic

cmslpc160:belforte$ crab submit ~/WORK/CRAB3/TC3/crabConfig.py
Will use CRAB configuration file /uscms/home/belforte/WORK/CRAB3/TC3/crabConfig.py
Error executing voms-proxy-info --actimeleft --timeleft --file /uscms/home/belforte/x509up_u6423:
43178


Log file is /tmp/belforte/crab_20211209_100704/crab.log

because the No VOMS attributes found! was actually printed by voms-proxy-info itself.

[belforte]

older versions of the client (crab-pre as of this writing) were falling back to forcing a new proxy creation in this case, but I think that a clear message and a clean failure is better. Users should learn never to use voms-proxy-init w/o a -voms argument (nor use the dreaded grid-proxy-init).