fix: add pip to builder/Dockerfile

[nestoracunablanco]

To ensure early failure in the unit tests, it is necessary to verify the installation of the Python OpenShift package. One effective way to accomplish this is by using the pip show command. Therefore, we need to enhance the Dockerfile to include pip.

What this PR does / why we need it: Fail early

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 #

Special notes for your reviewer:

Release note:

[openshift-ci]

Hi @nestoracunablanco. Thanks for your PR.

I'm waiting for a kubevirt member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[ksimon1]

Hi @nestoracunablanco,
can you please elaborate why do you need to verify the installation of the Python OpenShift package?

[nestoracunablanco]

Hi @ksimon1,
for context, please refer to this PR, which explains why we need to perform this verification.
The issue with the automation/unit-test.sh script is that it executes several oc commands to apply namespaces and templates, followed by the execution of python scripts. If the python scripts fail, the preceding oc commands are done unnecessary.
Implementing a verification step to check if the package is installed would provide a quick and low-cost early validation.

[ksimon1]

@nestoracunablanco thanks for the explanation. Make sense to me 👍
/ok-to-test

[0xFelix]

/approve

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[ksimon1]

/lgtm

[nestoracunablanco]

/retest