v2_cart_model: allow archiving of destroyed gears

Adds cart model logic and two node config options to allow admins to
enable archiving of gears as they are destroyed, and to specify the
directory for archiving the gears.

Enterprise bug: 1092045
https://bugzilla.redhat.com/show_bug.cgi?id=1092045
Preventing rollback for PatchUserEnvVarsOp in case of gear creation
broker/node: Add parameter for gear destroy to signal part of gear creation
node archive: improve doc, config logic

Added more detailed documentation for `node.conf` options, updated
V2CartridgeModel#archive to handle `nil` setting for
`ARCHIVE_DESTROYED_GEARS_DIR`
delete partial/broken archive on "tar" command failure
Merge pull request #5743 from dobbymoodge/node_block_rollback

Merged by openshift-bot