Add missing dependencies to requirements.txt

Add missing dependencies to tools/init/test-requirements.txt
for running unit tests. Libraries are placed in test-
requirementss.txt rather than requirements.txt due to library
versions included within the snap; if the versions in requirements.txt
differ from whats installed in the snap from Ubuntu core then the snap
fails to build.

Closes-Bug: #1908610
Change-Id: I83d623db3a8d3cd8f328b42da4aff5b71f2f0520

tools/init/test-requirements.txt

@@ -1,5 +1,8 @@
+cryptography
 flake8
 mock
+oslo.serialization===3.1.1
 pylint
+python-dateutil===2.8.1
 pep8
 stestr