support odd Linux distros

examples/bitehist.py

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # bitehist.py	Block I/O size histogram.
 #		For Linux, uses BCC, eBPF. See .c file.

examples/disksnoop.py

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # disksnoop.py	Trace block device I/O: basic version of iosnoop.
 #		For Linux, uses BCC, eBPF. See .c file.

examples/vfsreadlat.py

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # vfsreadlat.py		VFS read latency distribution.
 #			For Linux, uses BCC, eBPF. See .c file.

tools/pidpersec

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # pidpersec	Count new processes (via fork).
 #		For Linux, uses BCC, eBPF. See .c file.

tools/syncsnoop

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # syncsnoop	Trace sync() syscall.
 #		For Linux, uses BCC, eBPF. Embedded C.

tools/vfscount

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # vfscount	Count some VFS calls.
 #		For Linux, uses BCC, eBPF. See .c file.

tools/vfsstat

-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # vfsstat	Count some VFS calls.
 #		For Linux, uses BCC, eBPF. See .c file.