grub: make boot RAID check Petitboot-compatible

[bgilbert]

Petitboot doesn't support -e and doesn't support testing for a bare device without a path component.

https://bugzilla.redhat.com/show_bug.cgi?id=1915540#c7

[openshift-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[bgilbert]

/hold

pending ppc64le testing

[jlebon]

/approve

[bgilbert]

ppc64le testing isn't ready yet, but this is believed to work and should be harmless. Let's get it into a build.

/hold cancel

[arithx]

/lgtm

[bgilbert]

Confirmed that this fixes ppc64le boot.

[manojnkumar]

/lgtm

[openshift-ci-robot]

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/lgtm

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[ravanelli]

/lgtm

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: arithx, bgilbert, cgwalters, jlebon, manojnkumar, ravanelli

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• OWNERS [arithx,bgilbert,cgwalters,jlebon]

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