FilesystemBackend test fails with File exists: '/tmp/blobs/'

While running tox -e parallel to debug #8975 (closed), i found the following error:

=================================== FAILURES ===================================                                                                                                                           [27/1853]
________________ FilesystemBackendTestCase.test_get_path_custom ________________
[gw1] linux2 -- Python 2.7.9 /builds/project-0/.tox/parallel/bin/python2.7

self = <test_fs_backend.FilesystemBackendTestCase testMethod=test_get_path_custom>

    def test_get_path_custom(self):
>       backend = _blobs.FilesystemBlobsBackend()

tests/blobs/test_fs_backend.py:104: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
src/leap/soledad/server/_blobs.py:70: in __init__
    os.makedirs(blobs_path)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

name = '/tmp/blobs/', mode = 511

    def makedirs(name, mode=0777):
        """makedirs(path [, mode=0777])
    
        Super-mkdir; create a leaf directory and all intermediate ones.
        Works like mkdir, except that any intermediate path segment (not
        just the rightmost) will be created if it does not exist.  This is
        recursive.
    
        """
        head, tail = path.split(name)
        if not tail:
            head, tail = path.split(head)
        if head and tail and not path.exists(head):
            try:
                makedirs(head, mode)
            except OSError, e:
                # be happy if someone already created the path
                if e.errno != errno.EEXIST:
                    raise
            if tail == curdir:           # xxx/newdir/. exists if xxx/newdir exists
                return
>       mkdir(name, mode)
E       OSError: [Errno 17] File exists: '/tmp/blobs/'

.tox/parallel/lib/python2.7/os.py:157: OSError