Document how to disable cache lookup with the ec2 inventory script

Not all Linode hosts have a private ip. This fixes an actual error that was happening because the generated list of private ips is empty when there isn't one.

Fixes #4875

s/seperate/separate/

http://en.wiktionary.org/wiki/separate

In order to simplify the workflow with the GCE modules, it's now
possible to add the parameters and project name as arguments to the
various GCE modules.

The inventory plugin also returns the IP of the host in
`ansible_ssh_host` so that you don't have to specify IPs into the
inventory file.

Some update to the documentation are also added.

Closes #5583.

Signed-off-by: Brian Coca <briancoca+ansible@gmail.com>

ec2_placement was missing from the inventory variables ec2.py was
producing.  Make sure that gets properly included rather than ignored.

update default EC2 exclude regions -- this should be the best configuration for most users, but some may still want to tweak.

If a user has full EC2 access but no RDS access, the user
should still be able to query the EC2 inventory, although
will not obtain any information about any RDS instances.

Move the ec2 cache files from a shared /tmp location to the
user's ansible tmp directory.

Move regions until after authentication; otherwise pyrax.regions is an empty tuple and no inventory is returned.

Eliminate the RAX_REGION environment variable; iterate through all regions available to an account and present servers in region groups; default to using server name to identify servers in groups; set ansible_ssh_host key for each server; utilize the _meta key to provide all the hostvars for each server; all grouping by web, db, sql, lb, app based on server name; pretty print JSON output for some human-readable inventory action

Add set_setting to alleviate requirement that ~/.pyrax.cfg exists

Add regions as a optional env var to narrow our inventory scope

Clean up

limit the number of connections to external cobbler server for performance.
Added use of cobbler.ini file to configure settings.

Tested against Cobbler 2.4.0

limit the number of connections to external cobbler server for performance.
Added use of cobbler.ini file to configure settings.

Tested against Cobbler 2.4.0