Add ARCHIVA_CONTEXT_PATH env var

[ghost]

Hi. This PR would close #2.

Here is my container which I built using the Dockerfile in this PR.

https://hub.docker.com/r/josdotso/archiva-docker-prefixed/

Please note that the sed for ARCHIVA_CONTEXT_PATH only alters the configuration of the untar'ed Archiva source. If a previous config directory exists it will not be altered by this PR.

I tested that it works earlier this evening with Nginx reverse proxy config shown below.

# For more information on configuration, see:
#   * Official English Documentation: http://nginx.org/en/docs/
#   * Official Russian Documentation: http://nginx.org/ru/docs/

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;

events {
    worker_connections 1024;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;

    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    # include /etc/nginx/conf.d/*.conf;

    server {
        listen       443;
    server_name  example.org;

        ssl on;
        ssl_certificate      /etc/nginx/ssl/nginx.crt;
        ssl_certificate_key  /etc/nginx/ssl/nginx.key;
    ssl_session_cache  builtin:1000  shared:SSL:10m;
    ssl_protocols  TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers  HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
    ssl_prefer_server_ciphers  on;

    access_log  /var/log/nginx/archiva.access.log;

    location ^~  /archiva/ {
        proxy_set_header  Host $host;
        proxy_set_header  X-Real-IP $remote_addr;
        proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header  X-Forwarded-Proto $scheme;
        # Fix the “It appears that your reverse proxy set up is broken" error.
        proxy_read_timeout  90;
        proxy_pass          http://archiva.service.consul:4707/archiva/;
    }
    }
}

[benjamin-heasly]

Nice one. LGTM. 👍

Thanks for the PR!

Sorry for the delay.