Add ModifyInstanceAttribute to minimum required permissions
Add ModifyInstanceAttribute to minimum required permissions

[#153331539](https://www.pivotaltracker.com/story/show/153331539)

Signed-off-by: Luan Santos <509a85c757dc22c0257f4655fb3fb682d42f965b@pivotal.io>

cloudfoundry-incubator/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release,cloudfoundry-incubator/bosh-aws-cpi-release