* tools: use printb for more python3 compat

Switch to printb in killsnoop and wakeuptime

* tests: use subproceess sleep to trigger test

In some python implementations, time.sleep uses select instead of
nanosleep and hence won't trigger the bpf kprobe.

* tools: remove explicit python3 shebang

Use an ambiguous python invocation in the shebang line. Instead, rely on
packaging stage to mangle the line to specify a python version.

* cmake: add ENABLE_LLVM_SHARED option

This adds an option to specify that only the dynamic libraries should be
used to link bcc. This is most likely to be used in systems that don't
build/provide the llvm-static and clang-static package options
(fedora-based).

* rpm: enable llvm_shared and python3 build options

Enable rpm packaging with two new features:
 - shared-only packaging (no static linking)
 - python3
To enable these build features (off by default), run:
 RPM_WITH_OPTS="--with llvm_shared --with python3" ./scripts...