New flag --namespace-iam-role-key and the ability to request a role at the namespace level

[vladiacob]

The possibility to assign a specific role at the namespace level. A new flag to specify under which annotation the iam role is present at the namespace level.

[coveralls]

Coverage increased (+1.4%) to 20.874% when pulling f6a26876331df3effca42fc65f27ff98c909cf05 on vladiacob:role-on-namespace-level into 47b54ebf9908a5faeb4c25ff31df2e1e593c222e on jtblin:master.