GT-451 | Proper leader election and upgrade without using observe and TTL features

[nikita-vanyasin]

Based on https://github.com/arangodb/go-driver/pull/518 Generics added to simplify code for master URL.

[nikita-vanyasin]

I will have the same code in go-agency-helper

@informalict Not sure why it's need there, but feel free to copy the package. Also note that initial implementation proposed by Lars contains one small issue, it was fixed in this PR.

[informalict]

I will have the same code in go-agency-helper

@informalict Not sure why it's need there, but feel free to copy the package. Also note that initial implementation proposed by Lars contains one small issue, it was fixed in this PR.

because it must be used by ArangoSync, so there are 3 options:

• copy this logic into ArangoSync
• copy this logic to go-agency-helper and use it in ArangoSync. the go-agency-helper will be used by ArangoSync anyway because it will use poll functionality.
• create some public go-arangodb-helper where we can have public useful functions