ewaol-[distro,config,tests]: Add support for multiple VMs deployment

This patch brings up support for multiple EWAOL VMs, based on the same image
and kernel recipes. Each VM can have custom settings like rootfs extra space,
memory size and number of cpus. Currently, each VM has a different hostname,
based on its index: 'ewaol-vm1' for the first, 'ewaol-vm2' for the second, etc.

Number of VM instances is defined by 'EWAOL_VM_INSTANCES',
and is set to '1' by default.

For each VM following paremeters can be set:
 (*) EWAOL_VM*_ROOTFS_EXTRA_SPACE
 (*) EWAOL_VM*_MEMORY_SIZE
 (*) EWAOL_VM*_NUMBER_OF_CPUS

This patch also updates the default "*_TEST_GUEST_NAME" variables used by the
EWAOL runtime integration tests to 'ewaol-vm1'.

Issue-Id: SCM-3898
Signed-off-by: Kamil Dziezyk <kamil.dziezyk@arm.com>
Change-Id: Ib11e6edb7596b7ff75c930ef48fd15ba6cdfdc77