Tests: Raise exception if API cli_inband command fails.

Tests:  Raise exception if API cli_inband command fails.

* Configure tests to raise exception if cli_inband fails.
* Fix failing tests.
* Add filename detail to pcap.stat clib_error_return for debugging.

Note: this change identifies spurious issues with packet-generator such as:
  CliFailedCommandError: packet-generator capture: pcap file
  '/tmp/vpp-unittest-Test6RD-v09RPA/pg0_out.pcap' does not exist.

These issues resolve themselves on remaining test passes.

Change-Id: Iecbd09daee954d892306d11baff3864a43c5b603
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>