Add /keep_disks page to Admin menu.
Change underscores to camelcase in "kind" strings as documented.
Fix crash on error pages by removing before_filters that assume there
is a current_user.
Provide UUID prefix used for each schema in discovery document.
Use discovery document to build infix->kind map instead of using a
hard-coded list.
Update tests to match recent permission changes; dry up "404 if no
object found" logic; fix status codes in some error responses.
Do not run ec2 commands in test mode.
Ensure we always respond with json (except the redirect at the root
URI).

closes #1739
Always use symbol keys for object attribute names and string keys
inside serialized hashes, rather than HashWithIndifferentAccess.

This ensures serialized attributes go into the database as plain
hashes with string keys, even when Rails was responsible for
unserializing the data coming from the client.

refs #1944
refs #1987
Replace Admin menu with System menu (users can see those things too).
Add virtualMachine test fixture.
Change underscores to camelcase in "kind" strings as documented.
Do not offer to let non-admin users create new keepDisks and nodes.