Update dependent modules to support TF 0.12+

[Firaenix]

what

• Updated Null Label module to latest
• Updated IAM role module to latest
• Fixed reference to capabilities to be a list, not a string

why

• Builds using this module werent working on TF 1.8,4

[Gowiem]

/terratest

[Gowiem]

/terratest

[Gowiem]

@Firaenix unfortunately, this module needs to be updated with our testing harness + overall latest practices. We'll need someone from the core or maintainer teams to carve out some time to do that. I'll bring this up, but just an FYI that it may take some time.

[mergify]

Important

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[Firaenix]

@Firaenix unfortunately, this module needs to be updated with our testing harness + overall latest practices. We'll need someone from the core or maintainer teams to carve out some time to do that. I'll bring this up, but just an FYI that it may take some time.

No skin off my back, I'm just pointing to my fork of it atm. Just thought I'd merge back onto master.