rewrite "host" functionality, replacing it with base url

[cyberw]

There are a couple of issues with the host parameter functionality:

• A locustfile shouldnt have to specify a dummy host value if all URLs are absolute (host should be a convenience function, not a requirement). It gets even weirder to have this requirement for non-HTTP Users.
• Being able to specify a base url (http://asdf.com/**more_stuff**) instead of a bare host name would be very useful, and right now that doesnt work
• The name is misleading (as the user needs to specify protocol as well, and include a slash either at the end of host or the beginning of the request, causing issues like Malformed urls when passing a relative path without initial slash to HttpSession.get and similar methods #1262)

I suggest:

• Deprecate --host (and make it non-mandatory)
• Introduce a --base-url / -b parameter that automatically appends a "/" at the end and supports browser-style "root" urls.

So if base_url is http://x.com/foo

• self.client.get("bar") -> http://x.com/foo/bar
• self.client.get("/baz") -> http://x.com/baz

Some special cases:

• self.client.get("") -> http://x.com/foo
• self.client.get("?xyz") -> http://x.com/foo?xyz
• base_url = http://x.com/, self.client.get("/foo") -> http://x.com/foo (not http://x.com//foo)

[lhupfeldt]

Relates to #1467

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[github-actions]

This issue was closed because it has been stalled for 10 days with no activity. This does not necessarily mean that the issue is bad, but it most likely means that nobody is willing to take the time to fix it. If you have found Locust useful, then consider contributing a fix yourself!