pull-svn.py fails to sync revisions when SVN credentials is not setup

pull-svn.py fails to sync revisions when SVN credentials is not setup
https://bugs.webkit.org/show_bug.cgi?id=149941

Reviewed by Chris Dumez.

Added the support for specifying subversion credentials.

Also added the support for pulling from multiple subversion servers. Subversion servers are specified
in a JSON configuration file specified by --svn-config formatted as follows:

[
    {
        "name": "WebKit",
        "url": "http://svn.webkit.org/repository/webkit",
        "username": "webkitten",
        "password": "webkitten's password",
        "trustCertificate": true,
        "accountNameFinderScript":
            ["python", "/Volumes/Data/WebKit/Tools/Scripts/webkit-patch", "find-users"]
    },
    ...
]

In addition, refactored it to use the shared server config JSON for the dashboard access.

* tools/pull-svn.py:
(main): Now takes --svn-config-json, --server-config-json, --seconds-to-sleep and --max-fetch-count
as required options instead of seven unnamed arguments.
(fetch_commits_and_submit): Extracted from main. Fetches at most max_fetch_count new revisions from
the subversion server, and submits them in accordance with server_config.
(fetch_commit_and_resolve_author): Now takes a single repository dictionary instead of two separate
arguments for name and URL to pass down the repository's authentication info to fetch_commit.
(fetch_commit): Ditto. Add appropriate arguments when username and passwords are specified.
(resolve_author_name_from_account): Use a list argument instead of a single string argument now that
the argument comes from a JSON instead of sys.argv.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@190764 268f45cc-cd09-0410-ab3c-d52691b4dbfc