Koji buildArch task failed with {{{OSError: [Errno 30] Read-only file system: '/var/tmp/koji/tasks/7078'}}}

See Koji task #7137078

{{{
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/koji/daemon.py", line 1161, in runTask
response = (handler.run(),)
File "/usr/lib/python2.7/site-packages/koji/tasks.py", line 155, in run
self.createWorkdir()
File "/usr/lib/python2.7/site-packages/koji/tasks.py", line 181, in createWorkdir
os.makedirs(self.workdir)
File "/usr/lib/python2.7/os.py", line 150, in makedirs
makedirs(head, mode)
File "/usr/lib/python2.7/os.py", line 157, in makedirs
mkdir(name, mode)
OSError: [Errno 30] Read-only file system: '/var/tmp/koji/tasks/7078'
}}}