usertools/telemetry: provide info on available sockets

usertools/telemetry: provide info on available sockets

When a user runs the dpdk-telemetry script and fails to connect because
the socket path does not exist, run a scan for possible sockets that
could be connected to and inform the user of the command needed to
connect to those.

For example:

  $ ./dpdk-telemetry.py -i4
  Connecting to /run/user/1000/dpdk/rte/dpdk_telemetry.v2:4
  Error connecting to /run/user/1000/dpdk/rte/dpdk_telemetry.v2:4

  Other DPDK telemetry sockets found:
  - dpdk_telemetry.v2  # Connect with './dpdk-telemetry.py'
  - dpdk_telemetry.v2:2  # Connect with './dpdk-telemetry.py -i 2'
  - dpdk_telemetry.v2:1  # Connect with './dpdk-telemetry.py -i 1'

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Ciara Power <ciara.power@intel.com>
Reviewed-by: Conor Walsh <conor.walsh@intel.com>