Clean up requirements a bit

* Drop osc from test-requirements (and lower-constraints)

  I'm not clear on where/how we use it; I think it was a hold-over from
  swift3?

* Pin python-keystoneclient in our py2-constraints

  Something sees to have changed with the pip resolver that means it
  keeps trying to install a newer, py3-only version for our py2 jobs.

Change-Id: Ie37ac077517e1ece5fa6bf163d1ab5e316ced509

lower-constraints.txt

@@ -62,7 +62,6 @@ python-keystoneclient==2.0.0
 python-mimeparse==1.6.0
 python-subunit==1.2.0
 python-swiftclient==3.2.0
-python-openstackclient==3.12.0
 pytz==2018.3
 PyYAML==3.12
 requests==2.14.2

py2-constraints.txt

@@ -70,3 +70,4 @@ greenlet===0.4.15
 oslo.utils===3.42.1
 gitdb===0.6.4
 gitdb2===2.0.6
+python-keystoneclient===3.22.0

test-requirements.txt

@@ -12,7 +12,6 @@ os-testr>=0.8.0 # Apache-2.0
 mock>=2.0 # BSD
 python-swiftclient>=3.2.0
 python-keystoneclient!=2.1.0,>=2.0.0 # Apache-2.0
-python-openstackclient>=3.12.0
 boto>=2.32.1
 boto3>=1.9
 botocore>=1.12