Upgrade utils | change variables, errors and log prints to be general to both Containerized and NC environments

[romayalon]

Explain the changes

1. Converted Container/Server terms usage from upgrade_utils.js should_upgrade() and load_required_scripts() and instead used current_version and existing_version since it's being used by both Containerized and NC environments and Container can't be used in NC env.

Issues: Fixed #xxx / Gap #xxx

1. Fixed bullet 12 of NC | Online upgrade improvements #8586

Testing Instructions:

Manual tests -

1. Nothing to upgrade -
   a. Run sudo node noobaa-core/src/cmd/nsfs.js --debug 5, CTRL + C
   b. Run noobaa-cli upgrade start --expected_version 5.18.0 --expected_hosts hostname1
   Check the logs and see that container term was removed -
   Jan-16 11:11:04.197 [/13595] [L0] core.upgrade.upgrade_utils:: the versions of the new_version and the current_version match. no need to upgrade

2. Upgrade is needed -
   a. git checkout 5.17, Run sudo node noobaa-core/src/cmd/nsfs.js --debug 5, CTRL + C
   b. git checkout 5.18.0, Run sudo node noobaa-core/src/cmd/nsfs.js --debug 5, CTRL + C
   c. Run noobaa-cli upgrade start --expected_version 5.18.0 --expected_hosts hostname1
   Check the logs and see that container term was removed -
   Jan-16 11:15:28.699 [/15525] [L0] core.upgrade.upgrade_utils:: new_version is 1.0.0 and current server version is 0.0.0. will upgrade

3. Downgrade (artificial because 5.17 does not contain these changes) -
   a. change package.json version to 5.19, Run sudo node noobaa-core/src/cmd/nsfs.js --debug 5, CTRL + C
   b. git checkout 5.18.0, Run sudo node noobaa-core/src/cmd/nsfs.js --debug 5, CTRL + C
   Check the logs and see that container term was removed -

an-16 11:18:49.191 [nsfs/16419] [ERROR] core.upgrade.upgrade_utils:: the new_version (5.18.0) appears to be older than the current server version (5.19.0). cannot downgrade
Jan-16 11:18:49.191 [nsfs/16419] [ERROR] CONSOLE:: nsfs: exit on error Error: attempt to upgrade to an older version while server's version is newer
    at should_upgrade (noobaa-core/src/upgrade/upgrade_utils.js:57:15)
    at NCUpgradeManager.update_rpm_upgrade (noobaa-core/src/upgrade/nc_upgrade_manager.js:72:14)
    at async main (noobaa-core/src/cmd/nsfs.js:331:17)

• Doc added/updated
• Tests added

[shirady]

LGTM