Increase ping timeout on scenario testing

Some gating may fail because ping timeout is short (20s).
In this commit,  we will increase up to 60s.

- Added ping_timeout for compute config with default 60s
- Replaced hardcorded ssh timeout value with ssh_timeout

Fixes bug 1194026

Change-Id: If4e64aff17fc9aea1b6de03c684dff145ef5e6f2
diff --git a/tempest/config.py b/tempest/config.py
index d9de205..68acdaa 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -160,6 +160,10 @@
     cfg.StrOpt('ssh_user',
                default='root',
                help="User name used to authenticate to an instance."),
+    cfg.IntOpt('ping_timeout',
+               default=60,
+               help="Timeout in seconds to wait for ping to "
+                    "succeed."),
     cfg.IntOpt('ssh_timeout',
                default=300,
                help="Timeout in seconds to wait for authentication to "