Fix -install-velero flag for e2e tests

[jaidevmane]

Thank you for contributing to Velero!

Please add a summary of your change

1.adding install flag to test makefile
2.fixing bug where velero was being uninstalled in the APIGroup test even though the -install-velero flag was set to false

Does your change fix a particular issue?

Fixes #(issue)

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required.
• Updated the corresponding documentation in site/content/docs/main.

[dymurray]

LGTM. Please note this PR will be void if #3888 is merged as is.

It's likely untenable for each test to have to maintain the installVelero var, and Carilsia's PR will force that pattern to be rethought.

I will bring this up on the community call next week and figure out what the plan is to move forward.

[jenting]

LGTM