Lock congestion on metadata (ie prefix files)

[cstamas]

Affected version

All 2.0.x

Bug description

There is a lock congestion happening when prefix files are being discovered.

Problem: as many repositories are in play, all will be asking for .meta/prefixes.txt metadata, and named locks does not have "context" like repository is (see #1610 )

This is most visible in parallely executed Maven ITs:

Error:  Error executing Maven.
Error:  Could not acquire shared lock for [.meta-SLASH-prefixes.txt] using lock file:///D:/a/maven/maven/its/core-it-suite/target/user-home/.m2/repository/.locks/metadata~.meta-SLASH-prefixes.txt.lock in 30 SECONDS