get_file_mtime test fails on riscv

FAIL: breezy.tests.per_tree.test_get_file_mtime.TestGetFileMTime.test_get_file_mtime(PreviewTree)
----------------------------------------------------------------------
Traceback (most recent call last):
testtools.testresult.real._StringException: log: {{{
21599.488 creating repository in file:///tmp/testbzr-XoGBHl.tmp/breezy.tests.per_tree.test_get_file_mtime.TestGetFileMTime.test_get_file_mtime%28PreviewTree%29/work/tree/.bzr/.
21602.885 creating branch <breezy.bzr.branch.BzrBranchFormat8 object at 0x2011e3ba10> in file:///tmp/testbzr-XoGBHl.tmp/breezy.tests.per_tree.test_get_file_mtime.TestGetFileMTime.test_get_file_mtime%28PreviewTree%29/work/tree/
21603.879 trying to create missing lock u'/tmp/testbzr-XoGBHl.tmp/breezy.tests.per_tree.test_get_file_mtime.TestGetFileMTime.test_get_file_mtime(PreviewTree)/work/tree/.bzr/checkout/dirstate'
21603.923 opening working tree u'/tmp/testbzr-XoGBHl.tmp/breezy.tests.per_tree.test_get_file_mtime.TestGetFileMTime.test_get_file_mtime(PreviewTree)/work/tree'
}}}

Traceback (most recent call last):
  File "/<<PKGBUILDDIR>>/breezy/tests/per_tree/test_get_file_mtime.py", line 44, in test_get_file_mtime
    'now: %f, mtime_file_id: %f' % (now, mtime_file_id))
  File "/usr/lib/python2.7/dist-packages/unittest2/case.py", line 702, in assertTrue
    raise self.failureException(msg)
AssertionError: False is not true : now: 1542581543.411009, mtime_file_id: 1542581548.808923