Migrate the preprov creds module to tempest lib

This commit migrates the preprovisioned credentials provider from
tempest/common into tempest/lib. As part of this 2 dependencies are
also migrated to lib: the InvalidTestResource exception class and the
tempest.common.fixed_network module.

Change-Id: Ib9e909aaaf81f7cb57e2382cec44598e918747b8
diff --git a/releasenotes/notes/migrate-preprov-creds-ef61a046ee1ec604.yaml b/releasenotes/notes/migrate-preprov-creds-ef61a046ee1ec604.yaml
new file mode 100644
index 0000000..aa5f71a
--- /dev/null
+++ b/releasenotes/notes/migrate-preprov-creds-ef61a046ee1ec604.yaml
@@ -0,0 +1,11 @@
+---
+features:
+  - The tempest module tempest.common.preprov_creds which is used to provide
+    credentials from a list of preprovisioned resources has been migrated into
+    tempest lib at tempest.lib.common.preprov_creds.
+  - The InvalidTestResource exception class from tempest.exceptions has been
+    migrated into tempest.lib.exceptions
+  - The tempest module tempest.common.fixed_network which provided utilities for
+    finding fixed networks by and helpers for picking the network to use when
+    multiple tenant networks are available has been migrated into tempest lib
+    at tempest.lib.common.fixed_network.