improvement and bug fix for condor

[Moelf]

Bug fix:

• listenany doesn't guarantee the port number, so we should use the portnum returned
• finalizer is bugged, isnull doesn't exist

Improvement:

• instead of doing --worker = <cookie>, we manually call start_worker(<cookie>) such that user can use -e "..." to pre-execute stuff. In my case, I want to patch Sockets.getipaddr() such that it skips internal private IP range.

This is possible because Julia stacks multiple -e command line options

This PR doesn't have impact on any other backend and is backward compatible for Condor

[Moelf]

as an example and for posterity:

julia> using ClusterManagers, Distributed

julia> addprocs(HTCManager(1); exeflags = `-e 'include("/home/jiling/.julia-htc/init.jl")'`)

content of init.jl:

using Sockets
import Sockets: getipaddr
function getipaddr(addr_type::Type{T}) where T<:IPAddr
    addrs = getipaddrs(addr_type)

    if length(addrs) == 0
        error("No networking interface available")
    end

    # Prefer the first IPv4 address, non private
    i = something(findfirst(ip -> ip isa IPv4 && !startswith(string(ip), "192.168")
                            , addrs), 1)
    return addrs[i]
end

[Moelf]

last time I think @tanmaykm looked at Condor related stuff

[kescobo]

I'm OK to merge this and add it to a release with #183