scripts: add bpftrace.sh

This script simplifies execution of bpftrace scripts
for SPDK application analysis. The script should be
invoked as:

scripts/bpftrace.sh `pidof spdk_tgt` script.bt

where 'script.bt' is the name of the bpftrace script
you wish to execute.

The script helps simplify the following:

1) replace __EXE__ markers in the bpftrace script with
   the full path of the spdk executable (required for
   usdt probes);  it uses /proc/<pid>/exe to get the
   full path
2) replace __PID__ markers in the bpftrace script with
   the PID of the spdk process under analysis - this
   allows for doing things like filtering system call
   counts for just the SPDK process
3) invoke bpftrace with the -p <pid> option

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ib271f26efe4ba326d951a7b30f61b22be755dda7
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/7710


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>