Lookaside cache operations retries
    
    Both upload and download network operations might fail
    and in this case, a retry mechanism was implemented.
    In case of failure, there is a delay and another attempt(s).
    Delays are increasing with every attempt.
    A new key 'lookaside_attempts' in the configuration is there
    to parameterize such behavior. It expresses a maximum number
    of attempts to try the operation. Without this key, fedpkg will work
    the same as before = single attempt.
    Values 'lookaside_attempts = 1' or 'lookaside_attempts = 0'
    effectively disable retries too.
    The second new key 'lookaside_delay' is the initial delay (in seconds)
    between attempts that is doubled with each iteration.
    
    JIRA: RHELCMP-11210
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>