Remove EC2 API from devstack

This all started with an investigation into Fedora's use of ecua2ools
package.  This package is a bit of a nightmare because it pulls in a
lot of other system-python packages.

For Ubuntu, this package was removed in
I47b7e787771683c2fc4404e586f11c1a19aac15c.  However, it is not
actually a "pure python" package as described in that change, in that
it is not installable from pypi.  I can't see how you could actually
run exercises/euca.sh on Ubuntu unless you installed euca2ools by hand
-- ergo I suggest it is totally unused, because nobody seems to have
reported problems.

In the mean time, ec2 api has moved to a plugin [1] anyway where the
recommendation in their README is to use the aws cli from amazon.

Thus remove all the parts related to EC2 and ecua2ools from base
devstack.

[1] https://git.openstack.org/cgit/openstack/ec2-api

Change-Id: I8a07320b59ea6cd7d1fe8bce61af84b5a28fb39e
diff --git a/exercise.sh b/exercise.sh
index 19c9d80..9067033 100755
--- a/exercise.sh
+++ b/exercise.sh
@@ -14,11 +14,11 @@
 # Run everything in the exercises/ directory that isn't explicitly disabled
 
 # comma separated list of script basenames to skip
-# to refrain from exercising euca.sh use ``SKIP_EXERCISES=euca``
+# to refrain from exercising foo.sh use ``SKIP_EXERCISES=foo``
 SKIP_EXERCISES=${SKIP_EXERCISES:-""}
 
 # comma separated list of script basenames to run
-# to run only euca.sh use ``RUN_EXERCISES=euca``
+# to run only foo.sh use ``RUN_EXERCISES=foo``
 basenames=${RUN_EXERCISES:-""}
 
 EXERCISE_DIR=$TOP_DIR/exercises