refactor AND bugfix

[wraithgar]

Two commits here, one is a refactor so that we could more easily find the bug, the second is the bugfix.

When installing a relative path into a workspace, arborist was trying to install it relative to the project root. This was ok before workspaces as that was the only place you could add new deps. With workspaces we need to now add new deps relative to the tree it's being added to. The second commit does this.

~/D/n/s/ws $ npm pkg delete dependencies.a -w b
{}
~/D/n/s/ws $ node ../../cli i ./workspaces/a -w b

up to date, audited 5 packages in 871ms

found 0 vulnerabilities
~/D/n/s/ws $ npm pkg get dependencies -w b
{
  "b": {
    "a": "file:../a"
  }
}
~/D/n/s/ws $ npm ls
[email protected] /Users/wraithgar/Development/npm/scratch/ws
├── [email protected] -> ./workspaces/a
└─┬ [email protected] -> ./workspaces/b
  └── [email protected] deduped -> ./workspaces/a

[wraithgar]

This was refactoring and cleanup trying to debug an issue, the bug still stands but this code allowed us to find where the bug starts, to be fixed later.