S3: Support for standalone pracc server

[delamonpansie]

pracc binary is installed alongside with arakooon and alba it's supposed to be started like pracc pracc.ini example of configuration is below

[pracc]
; uds_path = pracc_endpoint
; max_clients = 128
; max_read_buf_size = 67108864
; write_messages_delay = 0
; asynchronous_thread_pool_size = 0
; synchronous_thread_pool_size = 64
; proxy_ip = 127.0.0.1
; proxy_port = 10000
; manifest_cache_size = 10000
; asd_connection_pool_size = 5
; asd_partial_read_timeout_milliseconds = 25
; proxy_timeout_milliseconds = 5000
; try_populate_manifest_cache_with_empty_reads = true
; try_populate_fragment_cache_manifests = true
; aws_parallel_limit = 128
; log_level = info

[aws]
; if keys are empty, pracc will try get this values from .aws/credentials
; access_key_id = 
; secret_access_key =

[graphite]
; if no ip configured, no graphite export
; ip = 
; port = 2003
; freq = 30