dpdk plugins: bug fixes and improvements

dpdk plugins: bug fixes and improvements

- Do not return error in configuration callback, which will cause
  collectd to be stopped. Instead, report error in init callback, which
  will unload incorrectly configured plugin.
- Remove redundant ProcessType configuration option, which was always set to
  "secondary"
- Use functions from cf_util_get family for parsing config file
- In case of parsing errors perform plugin cleanup
- Correctly remove previously created shared memory object if user specified
  "SharedMemObj" option with different value than default
- Prevent segmentation fault in dpdk_shm_cleanup
- Change 'send_updated' and 'notify' variable types to _Bool

Change-Id: Id7dfc7f25d2cebf332d47bcd5afaaebf577945d6
Signed-off-by: Przemyslaw Szczerbik <przemyslawx.szczerbik@intel.com>