testiso: increase memory for PXE tests

The PXE test fails due to memory exhaustion while trying to fit the
initramfs and rootfs in memory, leading to initramfs failures.
Increase the memory for the testiso VM.

Co-authored-by: Dusty Mabe <dusty@dustymabe.com>

Author: jbtrystram

mantle/cmd/kola/testiso.go

@@ -810,6 +810,14 @@ func testPXE(ctx context.Context, inst platform.Install, outdir string) (time.Du
 	if err != nil {
 		return 0, errors.Wrapf(err, "creating QemuBuilder")
 	}
+
+	// increase the memory for pxe tests with appended rootfs in the initrd
+	// we were bumping up into the 4GiB limit in RHCOS/c9s
+	// pxe-offline-install.rootfs-appended.bios tests
+	if inst.PxeAppendRootfs && builder.MemoryMiB < 5120 {
+		builder.MemoryMiB = 5120
+	}
+
 	inst.Builder = builder
 	completionChannel, err := inst.Builder.VirtioChannelRead("testisocompletion")
 	if err != nil {