Bash completion: Fix missing parameters in completion

[fstab50]

if any of the following are entered after the main executable is called (i.e. anything but a resource name), bash completion never prompts for a resource name again:

• --profile
• --region

[fstab50]

Fine tuned bash completion for the following previous keywords:

• --instances
• --snapshots
• --volumes
• --images
• --subnets
• --secgroups