feat(template): wrap IPv6 addresses in []

[rlguarino]

Add formatIP helper function which will wrap IPv6 addresses
in [] and print IPv4 addresses as is.

Closes #828

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[k8s-reviewable]

This change is 

[rlguarino]

@k8s-ci-robot I've signed the CLA

[coveralls]

Coverage increased (+0.06%) to 46.523% when pulling 54f6729 on rlguarino:ross/2017-06-08T18-48-35-07-00 into d556cc0 on kubernetes:master.

[aledbf]

/lgtm

[aledbf]

@rlguarino thanks!