added new flag that lets users specify the availability zone they want their instances spawned in
added abstract method in base_agent, to keep interface up to date with implementors
added availability zone validation for EC2
added availability zone validation for GCE
passing zone info when spawning on-demand and spot instances in EC2
specifying passed in zone in GCE, and saving/restoring it in the locations.yaml file for when we shut instances down
updated AppScalefile template with zone info
passing over name of zone to use to the AppController
added separate code route for seeing if availability zones exist in euca, since it differs from ec2
merged with specify-zone-as-flag
checking if group and keyname are in AppScalefile via yaml instead of simple string check
Merge pull request #288 from shatterednirvana/smarter-keyname-group-checking

checking if group and keyname are in AppScalefile via yaml instead of simple string check
Merge pull request #287 from shatterednirvana/specify-zone-as-flag

Specify availability zone as a flag
Merge remote-tracking branch 'org/testing' into use-persistent-disks-in-aws