improve integration tests stability

[RafalSkolasinski]

What this PR does / why we need it:

Recently TestPrepack.test_text_alibi_explainer was failing a lot in the integration tests.
This PR is fixing it.

Which issue(s) this PR fixes:

Fixes #2408

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

None

[RafalSkolasinski]

/test ingeration

[RafalSkolasinski]

/test integration

[seldondev]

Thu Sep 10 13:01:28 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-2409/1.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2409 --build=1

[seldondev]

Thu Sep 10 13:01:38 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-2409/2.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2409 --build=2

[seldondev]

Thu Sep 10 13:02:19 UTC 2020
The logs for [integration] [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-2409/3.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2409 --build=3

[axsaucedo]

As discussed on slack, good to go
/approve

[seldondev]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: axsaucedo

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