make 6443 as a constant

[yuzhang17]

What this PR does / why we need it:We hardcode 6443 all over the place and it should be a constant

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #66

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

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[k8s-ci-robot]

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[yuzhang17]

/assign @justinsb

[chuckha]

/ok-to-test

[chuckha]

/assign

[chuckha]

looks fine, just one comment about running goimports on the files with updated imports

[chuckha]

The imports are broken up into sections and alphabetized:

* first the standard library

* then all the non stdlib imports

please run goimports over this file

[yuzhang17]

/assign @chuckha

[chuckha]

/approve

assigning amy for lgtm
/assign @amy

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chuckha, SharksZhang

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[amy]

/lgtm