This commit adds support for P4 device and
resource management by implementing:
 * key P4 entities as Python objects
 * a context class for turning P4 info files into context
 * common functions around P4
 * a manager class which exploits P4 entities and context to manage P4 devices
 * GetConfig() RPC
 * SetConfig() RPC, and
 * DeleteConfig() RPC
 * basic internal and unit tests

Signed-off-by: Georgios Katsikas <katsikas.gp@gmail.com>