Include namespace in display name with hyphen not colon

[davidholsgrove]

#31 changed the display name to include the kubernetes namespace (yey!)

When using the Kubernetes auth method to generate MSSQL Database credentials, I now get a username with v-kubernetes-{namespace}: prefix, e.g;

v-kubernetes-testing:v-GENPRD_0XA_LSTN-clie-cFbDNmp9WeGSJAo3hanx-1532477048

previously the equivalent MSSQL username would have been;

v-kubernetes-vault-aut-GENPRD_0XA_LSTN-clie-1qMciGW3fm0jNFAIGMTz-1531203590

Comparing the same credential generated while using the AWS auth method, I get;

v-aws-Role-Lab_ACP-AWS-GENPRD_0XA_LSTN-clie-e7L3UhmmeGCfKCQNwWlr-1532568250

While a colon in a user name is valid for MSSQL, some older applications don't accept this unfortunately.
Can we change the display name to be hyphen separated instead of colon separated, which would be consistent with (at least) AWS Auth?

[catsby]

Closing b/c #39 was merged 😄