Fix for ensuring old clusterwide webhook is deleted

[ukclivecox]

Fixes #2009

• Delete the webhook clusterwide configurations if they exist when installing by namespace

[seldondev]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[seldondev]

Fri Jun 26 09:14:53 UTC 2020
The logs for [lint] [2] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2013/2.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2013 --build=2

[seldondev]

Fri Jun 26 09:16:11 UTC 2020
The logs for [pr-build] [1] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2013/1.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2013 --build=1

[ukclivecox]

/test notebooks

[seldondev]

Fri Jun 26 09:33:33 UTC 2020
The logs for [notebooks] [3] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2013/3.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2013 --build=3

[seldondev]

@cliveseldon: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
notebooks	dbc1767	link	/test notebooks

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