bcc/python: Add support for API 'bpf_attach_perf_event_raw' in BPF python interface

bcc/python: Add support for API 'bpf_attach_perf_event_raw' in BPF python interface

Add python interface for attach_perf_event_raw to bcc.
The bpf_attach_perf_event_raw API provide flexibility to use
advanced features of perf events with BPF. Presently, this
API is available to use in BPF programs via C and C++ interface.
Patch enables support to use in python interface.

Patch also adds testcase under 'tests/python' which uses
the newly added python interface 'attach_perf_event_raw'.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>