Also make this API return a proper HTTP code (409 instead of 500).

Change-Id: I5d86878b5ed6142ed2630adee78c0867c49b663f

Or at least try to.

Some deployments just don't use root device hints, and this is okay.

However, other deployments need root device hints, and with fast
track mode in ramdisks, we created a situation where the node cache
could be updated by a human or software between the time the agent
was started, and the deployment was requested.

As a result, the agent has been updated to check if we have a hint
and if we don't, update the cache from the node lookup endpoint.

This is not needed when the inband deploy steps are executed, as
the process of updating the steps does force the node cache to be
updated.

Change-Id: I27201319f31cdc01605a3c5ae9ef4b4218e4a3f6
Story: 2008039
Task: 40701

Introducing new function _umount_all_partitions to reduce the size
of _install_grub2

Change-Id: I304468d57b10d677f2a9d58aec42a1bf414c6cba

When we added software raid support, we started calling bootloader
installation. As time went on, we ehnanced that code path for non
RAID cases in order to ensure that UEFI nvram was setup
for the instance to boot properly.

Somewhere in this process, we missed a possible failure case where
the iscsi client tgtadm may return failures. Obviously, the correct
path is to not call iscsi teardown if we don't need to.

Since it was always semi-opportunistic teardown, we can't blindly
catch any error, and if we started iSCSI and failed to tear the
connection down, we might want to still fail, so this change
moves the logic over to use a flag on the agent object which
one extension to set the flag and the other to read it and take
action based upon that.

Change-Id: Id3b1ae5e59282f4109f6246d5614d44c93aefa7c
Story: 2007937
Task: 40395

Shuffle some functions around and reduce size of _is_bootloader_loaded
moving logic out to a new function.

Change-Id: I9c10bf05186dcebb37f175d61bf4ac9ff86b6510

This has been a popular guidance, and diskimage-builder has recently
started following it.

Change-Id: I794c846fb191c15b0a30546bf64d624dfbde0fd4