VMware: Remove references to ebs_root from spawn()

spawn() contained an important boolean called ebs_root. This was True
for any spawn which contained a block device mapping. This no longer
has any meaning, and was confusing. This change removes references to
ebs_root, instead using block_device_info directly.

N.B. The block device mapping behaviour of the VMware driver is still
not correct, but fixing it is not the purpose of this patch. This
patch simply makes the existing behaviour easier to see.

N.B. test_spawn_mask_block_device_info_password in test_vmops.py
assumes internal details of spawn in order to cause a failure after
emitting a log message. In moving the log message we need to update
the dance this test does to ensure that spawn fails after the log
message, but not before.

This change has been split out of
https://review.openstack.org/#/c/87002/, which was written by Shawn
Hartsock.

partial blueprint vmware-spawn-refactor

Co-authored-by: Shawn Hartsock <hartsocks@acm.org>
Change-Id: I11b355a6b53194bc9f85f542b54c9fbb9c061e04
Merge "VMware: Remove references to ebs_root from spawn()"