Merge "migrate testing to ubuntu focal"

Author: Zuul

lower-constraints.txt

@@ -10,6 +10,7 @@ os-client-config==1.29.0 # Apache-2.0
 osc-lib==1.12.1 # Apache-2.0
 
 # test-requirements.txt
+pyflakes==2.1.1
 coverage==4.0 # Apache-2.0
 python-subunit==0.0.18 # Apache-2.0/BSD
 oslotest==1.10.0 # Apache-2.0

test-requirements.txt

@@ -3,6 +3,10 @@
 # process, which may cause wedges in the gate later.
 
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
+# remove this pyflakes from here once you bump the
+# hacking to 3.2.0 or above. hacking 3.2.0 takes
+# care of pyflakes version compatibilty.
+pyflakes>=2.1.1
 
 coverage>=4.0,!=4.4 # Apache-2.0
 python-subunit>=0.0.18 # Apache-2.0/BSD