Bundle of mason bug fixes

[jabraham17]

Fixes several small mason bugs I came across

• A MASON_REGISTRY like MASON_REGISTRY=myreistry, would break, this is different than most other kinds of variables like PATH and PKG_CONFIG_PATH

• Not all directories in MASON_CACHED_REGISTRY where always available (mason update needs to be run). This would cause mason add ... to give bad error messages. This PR fixes that by adding mason update --force (always update the repos) and adjusts the error message to tell users to do that

• mason update would assume the branch name for a given repo was master, which breaks when using modern git

• paratest

[Reviewed by @]