Remove mock as a test requirement and add PyYAML as requirement.

Now that we have moved to py36 and later runtimes, we no longer
need to use the third party mock library and can only use the standard
library unittest.mock instead.

Change-Id: I97219a6b3ca2cff88b8871458466825e79736f77
Signed-off-by: Gael Chamoulaud (Strider) <gchamoul@redhat.com>

lower-constraints.txt

@@ -45,7 +45,6 @@ linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
 mistral-lib==1.2.0
-mock==2.0.0
 monotonic==1.4
 mox3==0.25.0
 msgpack==0.5.6

requirements.txt

@@ -4,5 +4,5 @@
 
 pbr>=3.1.1 # Apache-2.0
 six>=1.11.0 # MIT
-
+PyYAML>=3.12 # MIT
 ansible-runner>=1.4.4 # Apache-2.0

test-requirements.txt

@@ -5,7 +5,6 @@
 openstackdocstheme>=1.20.0 # Apache-2.0
 hacking<0.12,>=0.11.0 # Apache-2.0
 
-mock>=2.0.0 # BSD
 coverage!=4.4,>=4.0 # Apache-2.0
 python-subunit>=1.0.0 # Apache-2.0/BSD
 sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD