I would like to set maximum number of junit tests which can fail
during build and the build is marked still as stable, as unstable or as failed.

I found this option in task plugin, compiler warnings plugin etc. but
not in jUnit reports.

see configuration section of Task Scanner plugin
http://hudson.gotdns.com/wiki/display/JENKINS/Task+Scanner+Plugin

and/or Warnings plugin http://hudson.gotdns.com/wiki/display/JENKINS/Warnings+Plugin