Bump openstacksdk minimum version

We depend on the newer release for some neutron features.

Change-Id: I11eb15bb7c1e2075f21c6c58d732c3b09e82236f
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Depends-on: https://review.opendev.org/c/openstack/releases/+/1001307

Author: stephenfin

requirements.txt

@@ -5,7 +5,7 @@
 cryptography>=2.7 # BSD/Apache-2.0
 cliff>=4.13.0 # Apache-2.0
 iso8601>=0.1.11 # MIT
-openstacksdk>=4.16.0 # Apache-2.0
+openstacksdk>=4.19.0 # Apache-2.0
 osc-lib>=4.6.0 # Apache-2.0
 oslo.i18n>=3.15.3 # Apache-2.0
 python-keystoneclient>=3.22.0 # Apache-2.0