Allow Users to set Erlang VM parameters

[humaite]

This commit fixes a regression with the new entry-point. Users in some case needed to modify VM parameters
directly from the command line (and not from vm.args).

see: https://github.com/ArweaveTeam/arweave-dev/issues/842

[JamesPiechota]

@humaite if the new recommended procedure is to modify vm.args.src rather than use -- then I think that's great. WE don't need to re-add --, we can just document the new procedure

[humaite]

@humaite if the new recommended procedure is to modify vm.args.src rather than use -- then I think that's great. WE don't need to re-add --, we can just document the new procedure

I think it will be required anyway if one wants to start more than one nodes. It will be easier using these parameters than using vm.args - at least until we find a better way.

[JamesPiechota]

I suck at reading bash scripts ... and so can't really understand if this works. (i.e. naively I don't see how we differentiate the args from before the separator from those after the separation). So I'll just approve the PR and trust that we hit any issues intesting!

[humaite]

Yeah. Shell scripting is not really a great language, even more when we are not using POSIX. Bash or zsh scripts are not compatible together for example, that's quite a mess. Anyway, I'm trying to write only POSIX script, this is the reason why I'm using test command in instead of [ or [[ (available only on bash IIRC) for example.

The function will read all the argument from a list of parameters ${*} until this list is empty. All parameters are pushed on the variable params, but when -- is found, then the content of this variable is moved to vm_params. This is done for all arguments, one by one (see shift). When the loop is over, then two environment variables are set: VM_PARAMS containing only the parameters for the VM and LOCAL_PARAMS mainly used for arweave.

Here the code in action:

######################################################################
# Ensure VM_PARAMS and LOCAL_PARAMS environment variables are unset
######################################################################
echo vm_params: ${VM_PARAMS}
echo local_params ${LOCAL_PARAMS}
# vm_params: 
# local_params:

######################################################################
# let parse "test 1 2 3". Only LOCAL_PARAMS variables should be set,
# by default, we only want to set arweave arguments, not the VM.
######################################################################
parse_args test 1 2 3
echo vm_params: ${VM_PARAMS}
echo local_params ${LOCAL_PARAMS}
# vm_params: 
# local_params: test 1 2 3

######################################################################
# let parse "-a -b -c -- 1 2 3 test", the first part, before "--"
# are the arguments for the VM and the rest (after "--") are arguments
# for arweave
######################################################################
parse_args -a -b -c -- 1 2 3 test
echo vm_params: ${VM_PARAMS}
echo local_params ${LOCAL_PARAMS}
# vm_params: -a -b -c
# local_params 1 2 3 test

######################################################################
# let try to see what's happening if we put more "--" separators.
# Only the last arguments are being used for arweave, the rest is 
# for the vm parameters.
######################################################################
parse_args -a -b -c -- 1 -- 2 -- 3 test
echo vm_params: ${VM_PARAMS}
echo local_params ${LOCAL_PARAMS}
# vm_params: -a -b -c 1 2
# local_params 3 test