AGENT-971: Add Agent-Based installer support for iSCSI

[bfournie]

Add support for booting off iSCSI. A new boot mode - ISCSI, is added and is used to boot both the agent ISO and the installed image.

In order to boot the final image using ISCSI the rootDeviceHint has been added to agent-config.yaml.

Requires openshift/installer#9356.

Note that iSCSI is only supported for dhcp since coreos-installer does not support --copy-network when using the ISCSI network, see coreos/coreos-installer#1389.

[openshift-ci]

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[bfournie]

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[bfournie]

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[bfournie]

/cc @adriengentil

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[bfournie]

Confirmed successful SNO installation using following settings:

export AGENT_E2E_TEST_BOOT_MODE=ISCSI
export OPENSHIFT_RELEASE_STREAM=4.18
export AGENT_NMSTATE_DHCP=true
export AGENT_MINIMAL_ISO=true
export AGENT_E2E_TEST_SCENARIO=SNO_IPV4_DHCP

[bfournie]

/test e2e-agent-compact-ipv4

[bfournie]

Confirmed successful multi-node installation using following settings:

export AGENT_E2E_TEST_BOOT_MODE=ISCSI
export OPENSHIFT_RELEASE_STREAM=4.18
export AGENT_MINIMAL_ISO=true
export AGENT_E2E_TEST_SCENARIO=COMPACT_IPV4_DHCP

Note that openshift/installer#9356 is required.

Results of testing with iSCSI:

$ oc get nodes
NAME       STATUS   ROLES                         AGE   VERSION
master-0   Ready    control-plane,master,worker   52m   v1.31.3
master-1   Ready    control-plane,master,worker   68m   v1.31.3
master-2   Ready    control-plane,master,worker   68m   v1.31.3

[core@master-0 ~]$ lsblk -S
NAME HCTL       TYPE VENDOR   MODEL          REV SERIAL                               TRAN
sda  0:0:0:0    disk QEMU     QEMU HARDDISK 2.5+ drive-scsi0-0-0-0                    
sdb  7:0:0:0    disk LIO-ORG  master-0      4.0  4972e62f-1081-4fae-a3f7-d93493639829 iscsi
sr0  2:0:0:0    rom  QEMU     QEMU DVD-ROM  2.5+ QM00003                              sata