[testlib] introduce a RepoAccess class to easily create connection and request Each RepoAccess hold a session for a user and three helper function to help create Connection, ClientConnection of WebRequest related to this session. related to #2920299

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile