Bitbucket dependencies should use credentials from environment variables

[antoine-sachet]

When creating a bitbucket_remote, the default user and password should be fetched from the environment variables. This is consistent with the current behaviour of github_remote or gitlab_remote which respectively use auth_token = github_pat() and auth_token = gitlab_pat().

This is easily fixed in install-bitbucket.R by changing:

bitbucket_remote <- function(repo, ref = "master", subdir = NULL,
                             auth_user = NULL, password = NULL,
                             sha = NULL, host = "api.bitbucket.org/2.0", ...)

to:

bitbucket_remote <- function(repo, ref = "master", subdir = NULL,
                             auth_user = bitbucket_user(), password = bitbucket_password(),
                             sha = NULL, host = "api.bitbucket.org/2.0", ...)

In fact it should really have been part of PR #344 but I only noticed it now. Until this is fixed, there is no way to install a private bitbucket repository since credentials are no longer passed to dependencies.