Closes #1166

Info

• Our interception of npm install --global (and other global npm commands) relies on us setting the prefix configuration via an environment variable.
• However, if a user (or script) explicitly provides a prefix at the command line via --prefix, that will override our environment variable.
• In those cases, our intercepted install will fail since the install will go to a different location than we expect.
• At the same time, explicitly providing a prefix is an advanced option that likely means the user is doing something intentional and not trying to do a "standard" global install.
• We shouldn't try to be smarter than the user, in these cases we should skip interception entirely to prevent unexpected errors.

Changes

• Updated the has_global_flag helper to has_global_without_prefix to check for both the presence of --global and the absence of --prefix

Tested

• Added a unit test that covers each of the global commands and confirms that the parser disables global interception when an explicit prefix is added.