Add image client build timeout config option

This patch Ibc4307b406b71db258975da90a39c1f51ad27e12 changed
the RestClient so that it does not use the
CONF.compute.build_timeout variable anymore.

For this reason, there is no way to specify a timeout for the image
client, which inherits the hardcoded 60 seconds timeout.

This patch introduces a config option for this. For consistency,
a config option was added for build interval as well.

Change-Id: I0ac5ead60c4dc5a0c04feee513ae299ca14bd38e
Partial-bug: #1394519
Closes-bug: #1407943
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 61c840b..2e1d6f3 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -278,8 +278,8 @@
 #build_interval = 1
 
 # Timeout in seconds to wait for an instance to build. Other services
-# that do not define build_timeout will inherit this value, for
-# example the image service. (integer value)
+# that do not define build_timeout will inherit this value. (integer
+# value)
 #build_timeout = 300
 
 # Should the tests ssh to instances? (boolean value)
@@ -620,6 +620,14 @@
 # http accessible image (string value)
 #http_image = http://download.cirros-cloud.net/0.3.1/cirros-0.3.1-x86_64-uec.tar.gz
 
+# Timeout in seconds to wait for an image to become available.
+# (integer value)
+#build_timeout = 300
+
+# Time in seconds between image operation status checks. (integer
+# value)
+#build_interval = 1
+
 
 [image-feature-enabled]