Pin to older grpc for ruby < 2.3

A new version of grpc was released which breaks our CI because we don't
have a newer ruby.

NOTE: also temporarily remove teh ubuntu job because it's broken.

Change-Id: Icb87ea9b4322f5eee97802970b4e215c2bbce8f7
Related-Bug: #1812105

.zuul.yaml

@@ -2,3 +2,11 @@
     templates:
       - puppet-openstack-library-jobs
       - release-notes-jobs-python3
+    check:
+      jobs:
+        - puppet-openstack-libraries-puppet-beaker-rspec-ubuntu-bionic:
+            voting: false
+    gate:
+      jobs:
+        - puppet-openstack-libraries-puppet-beaker-rspec-ubuntu-bionic:
+            voting: false

puppet-openstack_spec_helper.gemspec

@@ -39,6 +39,10 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'webmock'
   spec.add_dependency 'etcdv3'
 
+  # grpc 1.18 requires ruby >= 2.2
+  grpc_rspec_version = RUBY_VERSION < '2.3.0' ? '~> 0.9': '~> 1.0'
+  spec.add_dependency 'grpc', grpc_rspec_version
+
   # Force net-telnet 0.1.1 as 0.2.0 requires ruby >= 2.3.0 which
   # CentOS does not provide.
   spec.add_dependency 'net-telnet', ['= 0.1.1']