Due to the length of the job name and the tox target we run into an
uncommon limitation; the virtualenv that tox launches is nested in a
path that is too long. This leads to and error on our longest named
job which prevents tox from running at all.

This limitation is the limit for the line length of the first line
in a shell script. See `man execve` for more info. A quote from that
manpage: 'A maximum line length of 127 characters is allowed for the
first line in a #! executable shell script.'

Change-Id: I43fba2a5ff1890d699045496c9eaee5e849f3e75
Backport: Liberty
Partially-Implements: blueprint multinode-gate