Make test timeout a variable

Make the test timeout that governs how long the preparing for test
playbook wait for SSH connectivity before proceeding.

This value, typically would need to be a longer value on larger
guest images as they will take longer to deploy and potentially
they have more services that extend the boot-up time.

Change-Id: Id76a40be2b7aadbc4594fb619b7fcb70cc2c9b2a

playbooks/roles/bifrost-prepare-for-test-dynamic/README.md

@@ -18,6 +18,9 @@ node_ssh_pause: The amount of time, defaulted to 4 seconds, to pause
                 useeful if the test image has a tendency to have
                 networking restart after sshd has started.
 
+wait_timeout: The number of seconds to wait for SSH connectivity to
+              the test machine to be established before proceeding.
+
 Dependencies
 ------------
 

playbooks/roles/bifrost-prepare-for-test-dynamic/defaults/main.yml

@@ -1,2 +1,3 @@
 ---
 node_ssh_pause: 10
+wait_timeout: 900

playbooks/roles/bifrost-prepare-for-test-dynamic/tasks/main.yml

@@ -13,7 +13,7 @@
 # limitations under the License.
 ---
 - name: "Waiting for the base testvm machine to become available."
-  wait_for: state=started port=22 host={{ ipv4_address }} timeout=900
+  wait_for: state=started port=22 host={{ ipv4_address }} timeout={{ wait_timeout }}
   when: ipv4_address is defined
 - name: "Pausing for 4 seconds to allow testvm to become fully operational and to avoid any potential sshd startup race."
   # NOTE(TheJulia): AFAIK sshd opens it's socket and then loads/generates