Added and mounted to the session a trasport adapter in the constructor.

Requests use transport adapters to define and maintain connections.
Http adapter has a parametr max_retries - maximum number of retries
each connetion shoult attempt when connection fails. Due to default
max_retries=0 after the connection faluire/closure/timeout/other
reason no other retries are permitted and BadStatusline error is
raised. In order to avvoid this issue number of retries were increased.
Using url as prefix instead specific 'https' prefix in order to handle http and https situations.
add pulp-admin group installation